Structure of the N-acetylpseudaminic acid-containing capsular polysaccharide of Acinetobacter baumannii NIPH67

Capsular polysaccharide (CPS) was isolated from a nosocomial pathogen Acinetobacter baumannii (A. baumannii) NIPH67 and studied by sugar analysis, Smith degradation, and ¹H and ¹³C NMR spectroscopy. The CPS was found to contain 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-l-manno-non-2-ulosonic acid (di-N-acetylpseudaminic acid, Pse5Ac7Ac), and the structure of the linear trisaccharide repeating unit of the CPS was established as →4)-α-Psep5Ac7Ac-(2→6)-β-d-Galp-(1→3)-α-d-GalpNAc-(1→. The genetic content of the capsule biosynthesis cluster of A. baumannii NIPH67, designated KL33, is consistent with the established CPS structure, and thus the capsule of the investigated strain was assigned to K33 group. Functions of proteins including two glycosyltransferases encoded by the genes of the K33 locus were assigned based on the structure of CPS and by the comparison with related proteins of other capsular types of A. baumannii.