Reidun Sirevåg

• Anglès d'Auriac, Marc B & Sirevåg, Reidun (2018). Multiplex PCR for the simultaneous detection of the Enterobacterial gene wecA, the Shiga Toxin genes (stx1 and stx2) and the Intimin gene (eae). BMC Research Notes.  ISSN 1756-0500.  11(360), s 1- 7 . doi: 10.1186/s13104-018-3457-8 Full text in Research Archive. Show summary

  The aetiology of several human diarrhoeas has been increasingly associated with the presence of virulence factors rather than with the bacterial species hosting the virulence genes, exemplified by the sporadic emergence of new bacterial hosts. Two important virulence factors are the Shiga toxin (Stx) and the E. coli outer membrane protein (Eae) or intimin, encoded by the stx and eae genes, respectively. Although several polymerase chain reaction (PCR) protocols target these virulence genes, few aim at detecting all variants or have an internal amplification control (IAC) included in a multiplex assay. The objective of this work was to develop a simple multiplex PCR assay in order to detect all stx and eae variants, as well as to detect bacteria belonging to the Enterobacteriaceae, also used as an IAC. The wecA gene coding for the production of the Enterobacterial Common Antigen was used to develop an Enterobacteriaceae specific qPCR. Universal primers for the detection of stx and eae were developed and linked to a wecA primer pair in a robust triplex PCR. In addition, subtyping of the stx genes was achieved by subjecting the PCR products to restriction digestion and semi-nested duplex PCR, providing a simple screening assay for human diarrhoea diagnostic.

• Lærum, Ole Didrik; Helsvig, Kim Gunnar & Sirevåg, Reidun (2009). The Norwegian Academy of Science and Letters: current revival of a time-honoured institution. International Journal of Technology Management.  ISSN 0267-5730.  46(1-2), s 27- 37
• Nederbragt, Alexander J; Balasingham, Anusha; Sirevåg, Reidun; Utkilen, Hans Chr.; Jakobsen, Kjetill S & Anderson-Glenna, Mary (2008). Multiple-locus variable-number tandem repeat analysis of Legionella pneumophila using multi-colored capillary electrophoresis. Journal of Microbiological Methods.  ISSN 0167-7012.  73(2), s 111- 117 . doi: 10.1016/j.mimet.2008.02.007
• Gulliksen, A; Solli, Lars Anders; Drese, KS; Karlsen, F; Sorensen, O; Karlsen, F; Rogne, H; Hovig, Johannes Eivind; Rogne, H; Hovig, E; Sirevåg, Reidun & Sirevag, R (2005). Parallel nanoliter detection of cancer markers using polymer microchips. Lab on a Chip.  ISSN 1473-0197.  5
• Gulliksen, Anja; Solli, Lars Anders; Drese, Klaus Stefan; Sørensen, Olaf; Karlsen, Frank; Rogne, Henrik; Hovig, Eivind & Sirevåg, Reidun (2005). Parallel nanoliter detection of cancer markers using polymer microchips. Lab on a Chip.  ISSN 1473-0197.  5(4), s 416- 420 Show summary

  A general multipurpose microchip technology platform for point-of-care diagnostics has been developed. Real-time nucleic acid sequence-based amplification ( NASBA) for detection of artificial human papilloma virus (HPV) 16 sequences and SiHa cell line samples was successfully performed in cyclic olefin copolymer (COC) microchips, incorporating supply channels and parallel reaction channels. Samples were distributed into 10 parallel reaction channels, and signals were simultaneously detected in 80 nl volumes. With a custom-made optical detection unit, the system reached a sensitivity limit of 10(-6) mu M for artificial HPV 16 sequences, and 20 cells mu l(-1) for the SiHa cell line. This is comparable to the detection limit of conventional readers, and clinical testing of biological samples in polymer microchips using NASBA is therefore possible.

• Eijsink, Vincent; Bjørk, Alexandra; Gåseidnes, Sigrid; Sirevåg, Reidun; Synstad, Bjørnar; Van den Burg, Bertus & Vriend, Gert (2004). Rational engineering of enzyme stability. Journal of Biotechnology.  ISSN 0168-1656.  113, s 105- 120
• Gulliksen, A; Solli, Christian; Solli, Lars; Karlsen, F; Rogne, H; Hovig, E; Hovig, Eivind; Nordstrøm, Trine; Nordstrom, T; Sirevag, R & Sirevåg, Reidun (2004). Real-time nucleic acid sequence-based amplification in nanoliter volumes. Analytical Chemistry.  ISSN 0003-2700.  76, s 9- 14
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitrios; Sirevåg, Reidun & Eijsink, Vincent (2004). Large improvement in the thermal stability of a tetrameric malate dehydrogenase by single point mutations at the dimer-dimer interface. Journal of Molecular Biology (JMB).  ISSN 0022-2836.  341, s 1215- 1226
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitris; Sirevåg, Reidun & Eijsink, Vincent (2004). Large improvement in the thermal stability of a tetrameric malate dehydrogenase by single point mutations at the dimer-dimer interface. Journal of Molecular Biology (JMB).  ISSN 0022-2836.  341, s 1215- 1226
• Eijsink, Vincent; Gåseidnes, Sigrid; Synstad, Bjørnar; Bjørk, Alexandra; Sirevåg, Reidun; Van den Burg, Bertus & Vriend, Gert (2004). Rational engineering of enzyme stability. Journal of Biotechnology.  ISSN 0168-1656.  113, s 105- 120
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitrios; Eijsink, Vincent G. H. & Sirevåg, Reidun (2003). Stabilization of a tetrameric malate dehydrogenase by introduction of a disulfide bridge at the dimer-dimer interface. Journal of Molecular Biology (JMB).  ISSN 0022-2836.  334, s 811- 821
• Bjørk, Alexandra; Mantzilas, Dimitrios; Sirevåg, Reidun & Eijsink, Vincent G. H. (2003). Electrostatic interactions across the dimer-dimer interface contribute to the pH-dependent stability of a tetrameric malate dehydrogenase. FEBS Letters.  ISSN 0014-5793.  553, s 423- 426
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitris; Eijsink, Vincent & Sirevåg, Reidun (2003). Stabilization of a tetrameric malate dehydrogenase by introduction of a disulfide bridge at the dimer-dimer interface. ?.  334, s 811- 821
• Bjørk, Alexandra; Mantzilas, Dimitris; Sirevåg, Reidun & Eijsink, Vincent (2003). A network of salt bridges contributes to the pH-dependent stability and oligomerization state of a tetrameric malate dehydrogenase. FEBS Letters.  ISSN 0014-5793.  553, s 423- 426
• Dalhus, Bjørn; Saarinen, Markuu; Sauer, Uwe H.; Eker, Per; Johansson, Kenth; Karlsson, Andreas; Ramaswamy, S.; Bjørk, Alexandra; Synstad, Bjørnar; Naterstad, Kristine; Sirevåg, Reidun & Eklund, Hans (2002). Structural basis for thermophilic protein stability: structures of thermophilic and mesophilic malate dehydrogenases. Journal of Molecular Biology (JMB).  ISSN 0022-2836.  318(3), s 707- 721 . doi: 10.1016/S0022-2836(02)00050-5 Show summary

  The three-dimensional structure of four malate dehydrogenases (MDH) from thermophilic and mesophilic phototropic bacteria have been determined by X-ray crystallography and the corresponding structures compared. In contrast to the dimeric quaternary structure of most MDHs, these MDHs are tetramers and are structurally related to tetrameric malate dehydrogenases from Archaea and to lactate dehydrogenases. The tetramers are dimers of dimers, where the structures of each subunit and the dimers are similar to the dimeric malate dehydrogenases. The difference in optimal growth temperature of the corresponding organisms is relatively small, ranging from 32 to 55 degreesC. Nevertheless, on the basis of the four crystal structures, a number of factors that are likely to contribute to the relative thermostability in the present series have been identified. It appears from the results obtained, that the difference in thermostability between MDH from the mesophilic Chlorobium vibrioforme on one hand and from the moderate thermophile Chlorobium tepidum on the other hand is mainly due to the presence of polar residues that form additional hydrogen bonds within each subunit, Furthermore, for the even more thermostable Chloroflexus aurantiacus MDH, the use of charged residues to form additional ionic interactions across the dimer-dimer interface is favored. This enzyme has a favorable intercalation of His-Trp as well as additional aromatic contacts at the monomer-monomer interface in each dimer. A structural alignment of tetrameric and dimeric prokaryotic MDHs reveal that structural elements that differ among dimeric and tetrameric MDHs are located in a few loop regions. (C) 2002 Elsevier Science Ltd. All rights reserved.

• Anglès d'Auriac, Marc B; Roberts, Hildegarde; Shaw, Terri; Sirevåg, Reidun; Hermansen, Leonila Fajardo & Berg, James D (2000). Field Evaluation of a Semiautomated Method for Rapid and Simple Analysis of Recreational Water Microbiological Quality. Applied and Environmental Microbiology.  ISSN 0099-2240.  66(10), s 4401- 4407 . doi: 10.1128/AEM.66.10.4401-4407.2000 Show summary

  An early warning system using a rapid enzymatic semi-automated method suitable for fecal coliform detection in recreational waters within 8 h, was developed further and evaluated in this study. This rapid method was compared to the standard method followed in the United Kingdom. We used 1011 samples originating from 206 different locations in Wales. When we assessed the presence orabsence of fecal coliforms, targeting very low levels of contamination, we obtained 83.9% agreement between the rapid method and the lauryl sulfate broth-membrane filtration technique, whereas direct confirmation of the samples processed by the rapid method showed 89.3% agreement. Environmental enzymatic background activity was found to be the main limiting factor for this method. Owing to a specific and integrated handling of the results by the software of the instrument, the percentage of false positives (a consequence of enzymatic background) was successfully limited to 2.9% by the direct confirmation evaluation. However 7.8% false negatives due to "late-growers" had to be accepted in order to produce results within a working day. At present, the method can be used in a more conservative way to assess the environmental threshold of 100 CFU of fecal coliforms per 100 ml in recreational waters. The implications of our findings with regard to the applicability of rapid enzymatic methods are discussed.

• Kolstø, Anne-Brit; Naterstad, K. & Sirevåg, Reidun (1995). Physical map of the genome of the green phototrophic bacterium Chlorobium tepidum. Journal of Bacteriology.  ISSN 0021-9193.  (177), s 5480- 5484
• Naterstad, K.; Kolstø, Anne-Brit & Sirevåg, Reidun (1995). Physical map of the genome of the green phototropic bacterium Chlorobium tepidum. Journal of Bacteriology.  ISSN 0021-9193.  177, s 5480- 5484

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• Østerud, Øyvind; Sirevåg, Reidun & Lærum, Ole Didrik (red.) (2009). Det Norske Videnskaps-Akademi Årbok 2008. Novus Forlag.  ISBN 9788270995547.  410 s.

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• Sirevåg, Reidun (2018). Diktatur kan være nyttig. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Sirevåg, Reidun (2018). Et bioteknologisk eventyr med store politiske følger. Aftenposten (morgenutg. : trykt utg.).  ISSN 0804-3116.
• Buchanan, Bob B.; Sirevåg, Reidun; Fuchs, Georg; Ivanovksy, Ruslan N.; Igarashi, Yasuo; Ishii, Masaharu; Tabita, F. Robert & Berg, Ivan A. (2017). The Arnon-Buchanan cycle; a retrospective, 1966-2016. Photosynthesis Research.  ISSN 0166-8595.  134(2), s 117- 131 . doi: 10.1007/s11120-017-0429-0
• Helsvig, Kim Gunnar; Sirevåg, Reidun & Lærum, Ole Didrik (2006). Norwegian Academy of Science and Letters. From National Policy to Global Science. Allea Biennial Yearbook.  s 121- 133
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitrios; Eijsink, Vincent G. H. & Sirevåg, Reidun (2004). Stabilization of a tetrameric malate dehydrogenase.
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitris; Eijsink, Vincent & Sirevåg, Reidun (2004). Stabilization of a tetrameric malate dehydrogenase.
• Eijsink, Vincent; Bjørk, Alexandra; Gåseidnes, Sigrid; Sirevåg, Reidun; Synstad, Bjørnar; Van den Burg, Bertus & Vriend, Gert (2004). Rational engineering of enzyme stability.
• Benestad, Ingun; Ytteborg, Elisabeth; Vanberg, Christin & Sirevåg, Reidun (2003). Two operons for chaperones in Chloroflexus aurantiacus.
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitrios; Eijsink, Vincent G. H. & Sirevåg, Reidun (2003). Engineering the stability and oligomerization state of a tetrameric malate dehydrogenase.
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitrios; Eijsink, Vincent G. H. & Sirevåg, Reidun (2003). Malate dehydrogenase from mesophilic and thermophilic green bacteria.
• Dalhus, Bjørn; Bjørk, Alexandra; Eijsink, Vincent G. H. & Sirevåg, Reidun (2003). Structural basis for protein thermostability; analysis of interactions within a protein oligomer and engeneering towards higher thermostability.
• Bjørk, Alexandra; Mantzilas, Dimitris; Sirevåg, Reidun & Eijsink, Vincent (2003). Stabilization of tetrameric malate dehydrogenase from Chloroflexus aurantiacus by engineering of an ionic network in the dimer-dimer interface.
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitrios; Eijsink, Vincent G. H. & Sirevåg, Reidun (2002). Engineering the stability and oligomerization state of a tetrameric malate dehydrogenase.
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitrios; Eijsink, Vincent G. H. & Sirevåg, Reidun (2002). STABILIZATION OF TETRAMERIC MALATE DEHYDROGENASE FROM CHLOROFLEXUS AURANTIACUS BY ENGINEERING AN IONIC NETWORK IN THE DIMER-DIMER INTERFACE.
• Bjørk, Alexandra; Mantzilas, Dimitrios; Dalhus, Bjørn; Eijsink, Vincent G. H. & Sirevåg, Reidun (2002). STABILIZATION OF TETRAMERIC MALATE DEHYDROGENASE FROM CHLOROFLEXUS AURANTIACUS BY ENGINEERING AN IONIC NETWORK IN THE DIMER-DIMER INTERFACE.
• Dalhus, Bjørn; Bjørk, Alexandra; Eijsink, Vincent G. H.; Mantzilas, Dimitrios & Sirevåg, Reidun (2002). Analysis of an ionic network within a protein oligomer and engeneering towards higher thermostability.
• Dalhus, Bjørn; Bjørk, Alexandra; Sirevåg, Reidun & Eklund, Hans (2002). Structural basis for protein thermostability - crystal structures of thermostable tetrameric malate dehydrogenases.
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitris; Eijsink, Vincent & Sirevåg, Reidun (2002). Stabilization of tetrameric malate dehydrogenase from Chloroflexus aurantiacus by engineering an ionic network in the dimer-dimer interface.
• Eijsink, Vincent; Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitris & Sirevåg, Reidun (2002). Engineering the stability and oligomerization state of a tetrameric malate dehydrogenase.
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitrios; Eijsink, Vincent G. H. & Sirevåg, Reidun (2001). Mutations at the dimer-dimer interface in tetrameric malate dehydrogenase from Chloroflexus aurantiacus have large effects on thermal stability.
• Dalhus, Bjørn; Bjørk, Alexandra; Eklund, Hans & Sirevåg, Reidun (2001). Crystal structures of MDHs from thermophilic bacteria: structural basis for protein thermostability.
• Dalhus, Bjørn; Bjørk, Alexandra; Sirevåg, Reidun & Eklund, Hans (2001). Crystal structure of MDHs from thermophilic bacteria - structural basis for thermophilic protein stability.
• Vanberg, Christin; Bjørk, Alexandra & Sirevåg, Reidun (2001). The moderate thermophilic green gliding bacterium Chloroflexus aurantiacus contains to alleles for chaperonins.
• Bjørk, Alexandra; Dalhus, Bjørn; Mantzilas, Dimitris; Eijsink, Vincent & Sirevåg, Reidun (2001). Mutations at the dimer-dimer interface in tetrameric malate dehydrogenase from Chloroflexus aurantiacus have large effects on thermal stability.
• Bjørk, Alexandra; Eijsink, Vincent G. H. & Sirevåg, Reidun (2000). Thermostability of tetrameric malate dehydrogenase from the green, gliding bacterium Chloroflexus aurantiacus.
• Vanberg, Christin; Bjørk, Alexandra & Sirevåg, Reidun (2000). Molecular chaperones from the moderate thermophilic, green gliding bacterium Chloroflexus aurantiacus.
• Bjørk, Alexandra; Molden, Tor; Torgunrud, Annette & Sirevåg, Reidun (1999). Thermostable malate dehydrogenases from phototrophic bacteria. Show summary

  In order to investigate the molecular basis of thermostability in proteins, we have isolated and characterized malate dehydrogenase (MDH) and its corresponding gene from mesophilic and thermophilic phototrophic bacteria. The green gliding bacterium Chloroflexus aurantiacus is a moderate thermophile which grows optimally at 55oC. The gene mdh coding for MDH from C. aurantiacus has been isolated characterized, cloned and overexpressed in Escherichia coli (1). The protein thus produced has been purified, crystallized and its 3-dimensional structure determined The native enzyme is a tetramer of identical subunits each with a molecular mass of 32.7 kDa . The enzyme is stable at 55oC, whereas at 65oC, the activity is reduced to the half after 9 min. An earler observation in this laboratory that tetramers are formed only when the temperature is approaching the optimum temperature of 55oC (2), has prompted us to examine specific amino acids in MDH for their role in subunit interactions as well as in thermostability. By in vitro mutagenesis, the following four mutants of mdh from C. aurantiacus have been constructed and then expressed in E. coli. : W39A, R173N, R173Q and Q188H. In each case, the overproduced protein have been tested for activity and thermostability and the results will be presented and discussed. Analysis and comparison of corresponding proteins from mesophilic and thermophilic organisms might give valuable information about amino acids important for thermostability and for subunit interactions. For this reason, MDH from the mesophilioc phototrophic bacterium Helibacterium gestii has been purified and characterized. Although H. gestii is a mesophile with an optimum temperature of growth of 37oC, its MDH is remarably thermostable. Thus, at 60oC, the half life, T1/2 of the enzyme is 20 min, whereas T1/2 for MDH from another mesophilic bacterium such as Chlorobium virioforme is 0.5 min at this temperature. The sequence of the 29 first amino acid in the N-terminal end of MDH from H. gestii has been determined and used to construct an oligomer which is used as a probe in order to find the mdh gene in a genomic library made in lambda-ZAP.. (1) Synstad et al. Arch Microbiol 165: 346-353 (1996) (2) Rolstad et al. J Bacteriol 170: 2947-2953 (1988) (3) Charnock et al. J Bacteriol 174: 1307-1313 (1992)

• Karlsen, Frank; Andreassen, Trine-Merethe; Rabone, Marian; Skrodenyte, Vesta; Sirevåg, Reidun; Eckner, Karl; D´Auriac, Marc Angles; Berg, James; Bergseth, Steinar & Charnock, Colin (1999). Development of molecular methods for rapid detection of coliform bacteria in water. Show summary

  The microbiological examination of drinking water has traditionally been performed by techniques such as membrane filtration (MF) and most probable number (MPN), using coliform bacteria as an indicator of fecal contamination. However, new methods such as those based on defined substrate technology are beginning to be accepted as well. Based on fluorescence measurements to assay the activity of b-galactosidase, Colifast ASA has developed an istrument, CA100 which automatically detects E. coli after 7-9 hours of growth in a specific enrichment medium. In addition, molecular methods based on the increasing knowledge of nucleic acid sequences, as well as immunological techniques, are being developed in several laboratories. In the present project, the enzymatic method developed by Colifast was compared with three molecular methods developed in our laboratory at UiO. For comparison and control purpose, traditional plate counts, biochemical tests and API 20E (Biomerieux) were included in the experiments. The first and second method utilise PCR (Polymerase Chain Reaction) after concentration of the samples by either centrifugation or by the aid of immunomagnetic beads coated with antibodies directed against E. coli. For identification of E. coli, a primer-pair was constructed which was shown to be E. coli specific both by homology search using Blast 2.0 (NCBI, USA) and by testing with PCR against 20 other commmon bacterial species. As a control of the the DNAS-quality, a universal primer-pair directed against a conserved region of the 16S rRNA gene was constructed and used in each experiment. The third method is a sandwich-ELISA (Enzyme-linked Immunoasorbent Assay) test, using antibodies against b-galactosidase. Samples included water from the Lysaker river as well as reconstituted freeze-dried reference cultures of defined composition.

• Molden, Tor; Bjørk, Alexandra; Tooming, Ave & Sirevåg, Reidun (1999). Thermostability in Chloroflexus aurantiacus. Show summary

  In order to investigate the molecular basis of thermostability in bacteria growing at high temperatures, we have isolated and characterized malate dehydrogenase (MDH) and its corresponding gene from several mesophilic and thermophilic phototrophic bacteria. The mdh gene from the moderate thermophile Chloroflexus aurantiacus has been isolated, characterized, cloned and overexpressed in Escherichia coli , and the 3-dimensional structure of the purified and crystallized protein thus produced has been determined. The native enzyme is a tetramer of identical subunits each with a molecular mass of 32.7 kDa. The enzyme is stable at its optimum temperature 55oC, but after 9 min at 65oC, the activity is reduced to half. An earlier observation in this laboratory which indicated that MDH exists as a tetramer only when the temperature is approaching the optimum temperature, has prompted us to examine the role of specific amino acids in subunit interactions as well as in thermostability. By in vitro mutagenesis, the four mutants W39A, R173N, R173Q and Q188H of mdh from C. aurantiacus have been constructed and expressed in E. coli.. The resulting mutant MDHs have been tested for activity, thermostability and ability to form tetramers. The results obtained will be presented and discussed. The possibility that cytoplasmic factors like molecular chaperones might be involved in the observed thermostability was examined. In addition to prevent aggregation of newly synthesized non-native polypeptides, chaperones are believed to prevent aggregation of proteins that unfold upon exposure of cells to stress, such as high temperature. When cell free extracts from C. aurantiacus grown at 45oC, 55oC, 60oC and 65oC were analyzed by SDS-PAGE, three distinct bands which increased in intensity with the growth temperature were detected. The bands corresponded to sizes of 11.2 kD, 60 kD and 75 kD and were detected also after heat treatment of the cell free extracts (60 min at 65oC) indicating that they are heat stable. The 60 kD band was eluted from the gel, purified and the sequence of the first 45 amino acids in the N-terminal end determined. Although no cross reaction occurred with antibodies directed against HSP 60 (GroEL) from Escherichia coli, the sequence showed an identity of 55.6% and a similarity of 76% with GroEL. A dendogram which shows the similarity of the present N-terminal sequence to the N-terminal sequences of HSP60 from 12 other organisms will be presented. .

• Molden, Tor; Bjørk, Alexandra; Tooming, Ave & Sirevåg, Reidun (1999). Thermostability in Chloroflexus aurantiacus. Show summary

  In order to investigate the molecular basis of thermostability in bacteria growing at high temperatures, we have isolated and characterized malate dehydrogenase (MDH) and its corresponding gene from several mesophilic and thermophilic phototrophic bacteria. The mdh gene from the moderate thermophile Chloroflexus aurantiacus has been isolated, characterized, cloned and overexpressed in Escherichia coli , and the 3-dimensional structure of the purified and crystallized protein thus produced has been determined. The native enzyme is a tetramer of identical subunits each with a molecular mass of 32.7 kDa. The enzyme is stable at its optimum temperature 55oC, but after 9 min at 65oC, the activity is reduced to half. An earlier observation in this laboratory which indicated that MDH exists as a tetramer only when the temperature is approaching the optimum temperature, has prompted us to examine the role of specific amino acids in subunit interactions as well as in thermostability. By in vitro mutagenesis, the four mutants W39A, R173N, R173Q and Q188H of mdh from C. aurantiacus have been constructed and expressed in E. coli.. The resulting mutant MDHs have been tested for activity, thermostability and ability to form tetramers. The results obtained will be presented and discussed. The possibility that cytoplasmic factors like molecular chaperones might be involved in the observed thermostability was examined. In addition to prevent aggregation of newly synthesized non-native polypeptides, chaperones are believed to prevent aggregation of proteins that unfold upon exposure of cells to stress, such as high temperature. When cell free extracts from C. aurantiacus grown at 45oC, 55oC, 60oC and 65oC were analyzed by SDS-PAGE, three distinct bands which increased in intensity with the growth temperature were detected. The bands corresponded to sizes of 11.2 kD, 60 kD and 75 kD and were detected also after heat treatment of the cell free extracts (60 min at 65oC) indicating that they are heat stable. The 60 kD band was eluted from the gel, purified and the sequence of the first 45 amino acids in the N-terminal end determined. Although no cross reaction occurred with antibodies directed against HSP 60 (GroEL) from Escherichia coli, the sequence showed an identity of 55.6% and a similarity of 76% with GroEL. A dendogram which shows the similarity of the present N-terminal sequence to the N-terminal sequences of HSP60 from 12 other organisms will be presented. .

• Tooming, Ave & Sirevåg, Reidun (1999). Induction of molecular chaperones in the thermophilic green bacterium Chloroflexus aurantiacus. Show summary

  The phototrophic green bacterium C. aurantiacus has an optimum temperature for growth of 55oC, but is capable of growth at temperatures up to 70oC. Earlier observations in our laboratory that addition of cell free extracts from C. aurantiacus increased the thermostability of purified malate dehydrogenase (MDH) from the same organism (1), prompted us to investigate this phenomenon in more detail. It was found that addition of cell free extracts from C. aurantiacus grown at temperatures above 55oC increased the thermostability of purified MDH significantly. Also MDH present in cell free extracts from cells grown at high temperatures was more thermostable than that in extracts from cells grown at low tempoeratures. The possibility that cytoplasmic factors such as molecular chaperones might be involved in maintenance of the observed thermostability was examined. Molecular chaperones are currently defined in purely fuctional terms as proteins that assist in the non-covalent assembly and/or disassembly of protein containig structures in vivo, but ar not componets of these structures when they are performing their normal biological functions (2). Molecular chaperones prevent protein aggregation by binding to exposed hydrophobic residues of newly synthesized non-native polypeptides. In addition, chaperones are believed to prevent aggregation in the case of proteins that unfold upon exposure of cells to stress, such as high temperature. Cell free extracts of C. aurantiacus grown at 45oC, 55oC, 60oC and 65oC were analysed by SDS-PAGE. Three distinct bands which increased in intensity with growth temperature were detected. These had molecular weights of 11.2 kDa, 60 kDa and 75 kDa and were present after heat treatment of the cell free extracts (60 min at 65oC), indicating that they are thermostable. When the gel was analysed by Western blotting, using antibodies directed against chaperonin hsp60 (GroEL) from Escherichia coli, no reaction occurred. However, when the 60 kDa band was eluted from the gel, purified and the first 45 amino acids of the N-terminal end sequenced, they showed a sequence identity of 55.6% and a similarity of 76% with GroEL from E. coli. A dendrogram will be presented which shows the sequence similarity of the present N-terminal end to the N-terminal ends of cnp60 from 12 other organisms. (1) Synstad, B., Emmerhoff, O., Sirevåg, R., 1996. Arch Microbiol 165, 346-543. (2) Ellis, R. J. 1977. Biochem Biophys Res Commun 238, 687-692.

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