Gene and putative protein structure of S-adenosylmethionine synthetase from Methanohalophilus portucalensis FDF1T

• Main Authors: Chia-Chen Lin, 林佳蓁
• Other Authors: 賴美津
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/42164988702568096394

碩士 === 國立中興大學 === 生命科學院碩士在職專班 === 100 === S-adenosylmethionine synthetase (SAMS, EC 2.5.1.6) can catalyse the formation of S-adenosylmethionine which is the major methyl donor from methionine and ATP. Halophilic methanoarchaeon Methanohalophilus portucalensis FDF1T can de novo synthesis glycine betaine by stepwise methylation of glycine by using SAM as the methyl donor. Metagenomic and comparative genomics analysis of genus Methanohalophilus revealed there are two sams genes. One of them located up stream of glycine betaine synthesizing gene cluster, named Mpsams1. The complete gene of Mpsams1 was cloned by Southern hybridization. The other sams were amplified from FDF1T chromosome DNA by PCR according to FDF1T metagenomic pyrosequencing databse, named Mpsams2. Amino acid sequence analysis and homology modeling structure of these two MpSAMS exhibit conserved methionine binding site, ATP binding site, Mg2+ and K+ binding site with other species, suggesting both possess catalytic activities of SAM formation. Sequence alignment and putative structure revealed MpSAMS2 displayed the amino acid substitution for the phosphate binding，Mg2+ binding、K+ binding sites which were important for SAMS activity in E. coli. However, these substitutions are conserved among archaeal SAMS. Phylogenetic analysis revealed MpSAMS1 was clustered with SAMS from eukaryote and bacteria, whereas MpSAMS2 was clustered with SAMS from archaea. We hypothesized that MpSAMS1 were horizontally transfered from bacteria, whereas MpSAMS2 were vertically obtained from archaeal ancestor.