Insights into the synthesis and ring size control of cyclic β-1,2-glucans

L. SOLEDAD GUIDOLIN

San Martín, Buenos Aires

Simposio; GlycoAR2019; 2019

UNSAM, Instituto Leloir, IBYME-CONICET, CIQUIBIC-CONICET

Cyclic β-1,2-glucans (CβG) are ring-shaped periplasmic homopolysaccharides that play an important role in the interaction between bacteria and eukaryotic cells in several symbiotic and pathogenic relationships. CβG are also interesting biotechnological molecules because of their chemical and immunomodulatory properties. In Brucella abortus, CβG are synthesized by CβG synthase (Cgs) a multimodular 320 KDa inner membrane protein that acts as a protein intermediate and catalyzes the four enzymatic reactions (initiation, elongation, phosphorolysis and cyclization) required for the synthesis of CβG. Several studies performed on Cgs allowed the identification and characterization of various catalytic and non-catalytic domains: a glycosyl-transferase domain responsible of the initiation and elongation reactions, a glycosyl-phosphorylase domain that regulates the degree of polymerization of the glucose chain, a cyclization domain that cyclizes and releases the CβG from the protein and a protein-protein interaction domain. Once CβG are synthesized in the cytoplasm by Cgs they are transported to the periplasm by a CβG transporter (Cgt) and succinylated by a CβG modifier (Cgm). These three integral inner membrane proteins form a CβG biosynthetic complex localized in the cell pole. The formation of the Cgs-Cgt-Cgm membrane complex could serve as a mechanism to maintain the fidelity of cyclic β-1,2-glucans biosynthesis and coordinate the synthesis with its transport and modification.