Structure and serological characteristics of the capsular K4 antigen of Escherichia coli O5:K4:H4, a fructose‐containing polysaccharide with a chondroitin backbone

Abstract

The chemical structure of the K4‐specific capsular polysaccharide (K4 antigen) of Escherichia coli O5:K4:H4 was elucidated by composition, carboxyl reduction periodate oxidation methylation nuclear‐magnetic‐resonance spectroscopy and enzymatic cleavage. The polysaccharide consists of a backbone with the structure → 3)‐β‐D‐glucuronyl‐(1,4)‐β‐D‐ N ‐acetylgalactosaminyl(1‐ to which β‐fructofuranose is linked at C‐3 of glucuronic acid. Mild acid hydrolysis liberated fructose and converted the K4 antigen into a polysaccharide which has the same structure as chondroitin. The defructosylated polysaccharide was a substrate for hyaluronidase and chondroitinase. The serological reactivity of the K4 polysaccharide was markedly reduced after defructosylation.