Rjm. Russell et al., THE CRYSTAL-STRUCTURE OF CITRATE SYNTHASE FROM THE THERMOPHILIC ARCHAEON, THERMOPLASMA-ACIDOPHILUM, Structure, 2(12), 1994, pp. 1157-1167
Background: The Archaea constitute a phylogenetically distinct, evolut
ionary domain and comprise organisms that live under environmental ext
remes 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 g
rowth temperature range 15-45 degrees C) may provide important informa
tion on the structural basis of protein thermostability. We have chose
n citrate synthase, the first enzyme of the citric acid cycle, as a mo
del enzyme for such studies. Results: We have determined the crystal s
tructure of Thermoplasma acidophilum citrate synthase to 2.5 Angstrom
and have compared it with the citrate synthase from pig heart, with wh
ich it shares a high degree of structural homology, but little sequenc
e identity (20%). Conclusions: The three-dimensional structural compar
ison of thermophilic and mesophilic citrate synthases has permitted ca
talytic and substrate-binding residues to be tentatively assigned in t
he archaeal, thermophilic enzyme, and has identified structural featur
es that may be responsible for its thermostability.