TETRAMERIC TRIOSEPHOSPHATE ISOMERASE FROM HYPERTHERMOPHILIC ARCHAEA

Triosephosphate isomerase (TIM) of the hyperthermophilic Archaea Pyroc occus wooesei and Methanothermus fervidus have been purified to homoge neity. The enzymes from the two hyperthermophiles represent homo-tetra mers of 100 kDa, contrary to all known bacterial and eukaryotic TIMs, which are dimers of 48-60 kDa, Molecular size determination of the TIM from the mesophilic methanogen Methanobacterium bryantii yielded the usual molecular mass of only 57 kDa, indicating that the tetrameric ag gregation state does not represent an archaeal feature but rather corr elates with thermoadaptation, A similar preference for higher protein aggregates in hyperthermophilic Archaea has previously been demonstrat ed for 3-phosphoglycerate kinases, The gene of the P. woesei TIM was c loned and sequenced, The archaeal TM proved to be homologous to its ba cterial and eukaryotic pendants, Most strikingly, the deduced protein sequence comprises only 224 residues and thus represents the shortest TIM sequence known as yet, Taking the three-dimensional structure of t he eucaryal TIM as a basis, from the shortenings of the chain consider able rearrangements at the bottom of the alpha/beta barrel and at its functionally inactive flank are expected, which are interpreted in ter ms of the formation of new subunit contacts.