Triosephosphate isomerase of the

The triosephosphate isomerase of the hyperthermophilic crenarchaeum Thermoproteus tenax (TtxTIM) represents a homomeric tetramer. Unlike the triosephosphate isomerases of other hyperthermophiles, however, the association of the TtxTIM tetramers is looser, allowing a reversible dissociation into inactive dimers. The dimer/tetramer equilibrium of TtxTIM is shifted to the tetrameric state through a specific interaction with glycerol-1-phosphate dehydrogenase of T. tenax, suggesting that higher oligomerization of the TtxTIM serves functional rather than stabilizing purposes. The main interest in the proteins of hyperthermophiles has been focused on the determinants of intrinsic thermostability. Numerous comparative analyses of crystal structures of homologous proteins from organisms with different optimal growth temperatures have been performed, uncovering an unexpected diversity of adaptationmechanisms of the various proteins [1–3]. Most of these rather general structural properties do not change uniformly in all proteins with ad