BACKGROUND: The structural basis of adaptation of enzymes to low temperature is poorly understood. Dimeric citrate synthase has been used as a model enzyme to study the structural basis of thermostability, the structure of the enzyme from organisms living in habitats at 55 degrees C and 100 degrees C having previously been determined. Here the study is extended to include a citrate synthase from an Antarctic bacterium, allowing us to explore the structural basis of cold activity and thermostability across the whole temperature range over which life is known to exit. RESULTS: We report here the first crystal structure of a cold-active enzyme, citrate synthase, isolated from an Antarctic bacterium, at a resolution of 2.09 A. In comparison with the same enzyme from a hyperthermophilic host, the cold-active enzyme has a much more accessible active site, an unusual electrostatic potential distribution and an increased relative flexibility of the small domain compared to the large domain. Several other features of the cold-active enzyme were also identified: reduced subunit interface interactions with no intersubunit ion-pair networks; loops of increased length carrying more charge and fewer proline residues; an increase in solvent-exposed hydrophobic residues; and an increase in intramolecular ion pairs. CONCLUSIONS: Enzymes from organisms living at the temperature extremes of life need to avoid hot or cold denaturation yet maintain sufficient structural integrity to allow catalytic efficiency. For hyperthermophiles, thermal denaturation of the citrate synthase dimer appears to be resisted by complex networks of ion pairs at the dimer interface, a feature common to other hyperthermophilic proteins. For the cold-active citrate synthase, cold denaturation appears to be resisted by an increase in intramolecular ion pairs compared to the hyperthermophilic enzyme. Catalytic efficiency of the cold-active enzyme appears to be achieved by a more accessible active site and by an increase in the relative flexibility of the small domain compared to the large domain.
==About this Structure==
==About this Structure==
1A59 is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Bacteria Bacteria]. The following page contains interesting information on the relation of 1A59 with [[http://pdb.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/pdb93_1.html Citrate Synthase]]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1A59 OCA].
1A59 is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Bacteria Bacteria]. The following page contains interesting information on the relation of 1A59 with [[http://pdb.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/pdb93_1.html Citrate Synthase]]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1A59 OCA].
==Reference==
Structural adaptations of the cold-active citrate synthase from an Antarctic bacterium., Russell RJ, Gerike U, Danson MJ, Hough DW, Taylor GL, Structure. 1998 Mar 15;6(3):351-61. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/9551556 9551556]
[[Category: Bacteria]]
[[Category: Bacteria]]
[[Category: Citrate Synthase]]
[[Category: Citrate Synthase]]
Line 29:
Line 25:
[[Category: Taylor, G L.]]
[[Category: Taylor, G L.]]
[[Category: Cold-activity]]
[[Category: Cold-activity]]
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 09:49:59 2008''
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Jun 26 17:02:22 2008''
1A59 is a Single protein structure of sequence from Bacteria. The following page contains interesting information on the relation of 1A59 with [Citrate Synthase]. Full crystallographic information is available from OCA.
