The crystal structure of citrate synthase from the thermophilic archaeon, Thermoplasma acidophilum.
BACKGROUND
The Archaea constitute a phylogenetically distinct, evolutionary domain and comprise organisms that live under environmental extremes of temperature, salinity and/or anaerobicity. Different members of the thermophilic Archaea tolerate temperatures in the range 55-110 degrees C, and the comparison of the structures of their enzymes with the structurally homogolous enzymes of mesophilic organisms (optimum growth temperature range 15-45 degrees C) may provide important information on the structural basis of protein thermostability. We have chosen citrate synthase, the first enzyme of the citric acid cycle, as a model enzyme for such studies.


RESULTS
We have determined the crystal structure of Thermoplasma acidophilum citrate synthase to 2.5 A and have compared it with the citrate synthase from pig heart, with which it shares a high degree of structural homology, but little sequence identity (20%).


CONCLUSIONS
The three-dimensional structural comparison of thermophilic and mesophilic citrate synthases has permitted catalytic and substrate-binding residues to be tentatively assigned in the archaeal, thermophilic enzyme, and has identified structural features that may be responsible for its thermostability.
Russell
R J
RJ
School of biology and Biochemistry, University of Bath, UK.
Hough
D W
DW
Danson
M J
MJ
Taylor
G L
GL
D000595:Amino Acid Sequence; D000818:Animals; D002950:Citrate (si)-Synthase / Q000737:chemistry*; D003196:Computer Graphics; D018360:Crystallography, X-Ray; D004795:Enzyme Stability; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid; D013552:Swine; D013822:Thermoplasma / Q000201:enzymology*
D002950:Citrate (si)-Synthase