The crystal structure of triosephosphate isomerase (TIM) from Thermtotoga maritima: A comparative thermostability structural analysis of ten different TIM structures

The molecular mechanisms that evolution has been employing to adapt to envi ronmental temperatures are poorly understood. To gain some further insight into this subject we solved the crystal structure of triosephosphate isomer ase (TIM) from the hyperthermophilic bacterium Thermotoga maritima (TmTIM), The enzyme is a tetramer, assembled as a dimer of dimers, suggesting that the tetrameric wild-type phosphoglycerate kinase PGK-TIM fusion protein con sists of a core of two TIM dimers covalently linked to 4 PGK units. The cry stal structure of TmTIM represents the most thermostable TIM presently know n in its SD-structure, It adds to a series of nine known TIM structures fro m a wide variety of organisms, spanning the range from psychrophiles to hyp erthermophiles, Several properties believed to be involved in the adaptatio n to different temperatures were calculated and compared for all ten struct ures. No sequence preferences, correlated with thermal stability, were appa rent from the amino acid composition or from the analysis of the loops and secondary structure elements of the ten TIMs, A common feature for both psy chrophilic and T. maritima TIM is the large number of salt bridges compared with the number found in mesophilic TIMs. In the two thermophilic TIMs, th e highest amount of accessible hydrophobic surface is buried during the fol ding and assembly process. Proteins 1999;37:441-453. (C) 1999 Wiley-Liss, I nc.