Novel glycoside hydrolase family enzymes from Escherichia coli are associated with osmo-regulated periplasmic glucan synthesis

Abstract

Most Gram-negative bacteria synthesize osmo-regulated periplasmic glucans (OPG) in the periplasm 22 or extracellular space. Many pathogens lose their pathogenicity by knocking out opgG, an OPG23 related gene indispensable for OPG synthesis. However, the biochemical functions of OpgG and OpgD, 24 a paralog of OpgG, have not been elucidated. In this report, structural and functional analyses of OpgG 25 and OpgD from Escherichia coli revealed that these proteins are β-1,2-glucanases with remarkably 26 different activity, establishing a new glycoside hydrolase family. Furthermore, a reaction mechanism 27 with an unprecedentedly long proton transfer pathway is proposed for OpgD. The conformation of the 28 region that forms the reaction pathway differs noticeably between OpgG and OpgD, which explains 29 the observed low activity of OpgG. The findings enhance our understanding of OPG biosynthesis and 30 provide insights into functional diversity for this novel enzyme family.