The structure of Klebsiella pneumoniae K108 capsular polysaccharide is similar to Escherichia coli colanic acid.

The clinical isolate of Klebsiella pneumoniae 1333/P225 was revealed as containing a KL108 K. pneumoniae K locus for capsule biosynthesis. The gene cluster demonstrated a high level of sequence and arrangement similarity with that of the E. coli colanic acid biosynthesis gene cluster. The KL108 gene cluster includes a gene of WcaD polymerase responsible for joining oligosaccharide K units into capsular polysaccharide (CPS), acetyltransferase, pyruvyltransferasefive and genes for glycosyltransferases (Gtrs), four of which have homologues in genetic units of the colanic acid synthesis. The fifth Gtr is specific to this cluster. The work involved the use of sugar analysis, Smith degradation and one- and two-dimensional H and C NMR spectroscopy to establish the structure of the K108 CPS. The CPS repetitive K unit is composed of branched pentasaccharide with three monosaccharides in the backbone and a disaccharide side chain. The main chain is the same as for colanic acid but the side chain differs. Two bacteriophages infecting K. pneumoniae strain 1333/P225 were isolated and structural depolymerase genes were determined; depolymerases Dep108.1 and Dep108.2 were cloned, expressed and purified. It was demonstrated that both depolymerases specifically cleave the β-Glcp-(1→4)-α-Fucp linkage between K108 units in the CPS.