Structure of the Escherichia coli K2 capsular antigen. Stereochemical configuration of the glycerophosphate and distribution of galactopyranosyl and galactofuranosyl residues

Abstract

The E. coli K2 capsular antigen is known to be composed of .alpha.-D-galactopyranosyl(1-2)glycerophosphate and .alpha.-D-galactofuranosyl(1-2)glycerophosphate units which are connected by phosphodiester bonds to C-4 of the galactopyranosyl and C-5 or C-6 of the galactofuranosyl moieties. The glycerophosphates were release by 2 different procedures and shown to have the sn-glycero-3-phosphate stereochemical configuration. In the 1st, the chain was fragmented by Smith degradation to glycerophosphothreitol from which the glycerophosphate was released by alkali hydrolysis. The structure-dependent low recovery of .alpha.-glycerophosphate (< 10%) initiated the development of another degradative sequence which consisted of periodate oxidation, .beta. elimination, hydrazinolysis and alkaline treatment. This way, .apprx. 90% of the glycerophosphate was released as sn-glycero-3-phosphate. .beta. Elimination revealed in addition that most of the galactofuranosyl residues carry the phosphodiester bond at position 5. Separation by gel permeation chromatography and analysis of the fragments obtained by .beta. elimination showed that pyranosidic and furanosidic galactosyl residues alternate in the same chain and suggested the sequences Galf(p)GroP-(GalpGroP)n-Galf- and -GalfGroP-(GalpGroP)n-Galf-, where n is 6, 4 and 3, respectively.