Nucleotide sequence of the glyceraldehyde‐3‐phosphate dehydrogenase gene from the mesophilic methanogenic archaebacteria Methanobacterium bryantii and Methanobacterium formicicum

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Abstract
The genes for glyceraldehyde‐3‐phosphate dehydrogenase (gap genes) from the mesophilic methanogenic archaebacteria Methanobacterium formicicum and Methanobacterium bryantii were cloned and sequenced. The deduced amino acid sequences show 95% identity to each other and about 70% identity to the glyceraldehyde‐3‐phosphate dehydrogenase from the thermophilic methanogenic archaebacterium Methanothermus fervidus. Although the sequence similarity between the archaebacterial glyceraldehyde‐3‐phosphate dehydrogenase and the homologous enzyme of eubacteria and eukaryotes is low, an equivalent secondary‐structural arrangement can be deduced from the profiles of the physical parameters hydropathy, chain flexibility and amphipathy. In order to find possible thermophile‐specific structural features of the enzyme from M. fervidus, a comparative primary‐sequence analysis was performed. Amino acid exchanges leading, to a stabilization of the main‐chain conformation, could be found throughout the sequence of the thermophile enzyme. Striking features of the thermophile sequence are the preference for isoleucine, especially in β‐sheets, and a low arginine/lysine ratio of 0.54.