Cloning of the key succinoglycan biosynthesis gene exoA and exoY from Agrobacterium sp. M-503 and the sequence analysis of encoding proteins

摘要

Succinoglycan is an acidic exopolysaccharide that is important for invasion of the nodules. It is a high-molecular-weight polymer consisting of repeating octasaccharide units. These units are synthesized by a complex pathway encoded by numbers of exo genes. In this study, two key genes, exoA and exoY, were cloned and sequenced, which controlled the first two glycosyltransferase reactions in the biosynthesis of succinoglycan. The sequences contained 999-base-pares (bp) and 681-bp Open reading Frame (ORF) encoding 332 and 236 amino-acid proteins with molecular weights of approximate 36.8 kDa and 25.5 kDa, respectively. The putative proteins, ExoA and ExoY, were analyzed by several online protein analysis softwares. The results showed ExoA and ExoY were the membrane proteins with three (ExoA) and one (ExoY) hydrophobic transmembrance domains. Their theoretical PI values were 9.49 and 9.34, respectively. The second structures analysis indicated that they were composed of 45.48% and 38.94% α-helix, 13.55% and 16.81% β-sheet, and 40.96% and 44.25% random coil structures respectively. These data will lay a foundation for the subsequent 3D structure prediction and gene mutation to improve succinoglycan production.