Lipopolysaccharide O-antigen is an attractive candidate for immunotherapeutic strategies targeting antibiotic-resistant Klebsiella pneumoniae. Several K. pneumoniae O-serotypes are based on a shared O2a-antigen backbone repeating unit;antigen is synthesized on undecaprenol diphosphate in a pathway involving the O2a polymerase, WbbM, prior to its export by an ABC transporter. This dual domain polymerase possesses a Cterminal galactopyranosyltransferase resembling known GT8 family enzymes, and an N-terminal DUF4422 domain identified here as a galactofuranosyltransferase defining a previously unrecognized family (GT111). Functional assignment of DUF4422 explains how galactofuranose is incorporated into various polysaccharides of importance in vaccine production and the food industry. In the 2.1 Å-resolution structure, three WbbM protomers associate to form a flattened triangular prism connected to a central stalk that orients the active sites towards the membrane.The biochemical, structural and topological properties of WbbM offer broader insight into the mechanisms of assembly of bacterial cell-surface glycans.

Highlights d a-Syn binds LC3 on the surface of MVB membranes d Mutant a-syn draws LC3 into detergent-resistant aggregates d Loss of LC3 function at MVBs leads to a-syn secretion via exosome d Restoration of LC3 activity promotes a-syn degradation Authors

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