Structure of K102 Capsular Polysaccharide from Acinetobacter baumannii KZ-1102 and Its Cleavage by Phage Cato Depolymerase

<i>Acinetobacter baumannii</i> is a significant nosocomial pathogen characterized by the ability to produce a wide variety of capsular polysaccharides (CPSs). The structures of a K102-type CPS isolated from <i>A. baumannii</i> KZ-1102 and its Smith degradation product were determined by sugar analysis, 1D and 2D ¹H NMR spectroscopy, and ¹³C NMR spectroscopy. The K102 CPS biosynthesis gene cluster (KL102) contains genes for common sugar synthesis, K unit processing, capsule export, glycosyl transfer, initiating sugar phosphate transfer, and genes that encode d-Glc<i>p</i>NAc/d-Gal<i>p</i>NAc dehydrogenase and phosphoglycerol transferase. The CPS is composed of a pentasaccharide repeating unit (K unit) consisting of a tetrasaccharide backbone including one α-d-Gal<i>p</i>, three α-d-Glc<i>p</i>NAc residues, and one residue of a β-d-Glc<i>p</i> as a side chain. The tailspike depolymerase of the specific <i>Obolenskvirus</i> phage Cato was found to cleave the α-d-Glc<i>p</i>NAc-(1→6)-α-d-Glc<i>p</i>NAc linkage in the K102 CPS to give the monomer and dimer of the K repeating unit, which were characterized by high-resolution electrospray ionization mass spectrometry as well as ¹H and ¹³C NMR spectroscopy.