A model for mucus glycoprotein structure

Abstract

An approximately 500,000Da subunit characterizes the structural glycoprotein of mucus. This unit is composed of a rod-like very heavily glycosylated protein chain with an unglycosylated cysteine rich region at its end. It is proposed that the ‘bare’ peptide portion of the subunit forms itself into a lectin by undergoing a disulfide bond stabilised conformational fold. The lectin binding site, R, is assumed to be selective for a rare sugar sequence, which, when present, creates a binding site R*. The site R* has to be relatively rare. The average number <s*> of sidechains which contain R* per subunit will only be of order 1. When <s*> ⩽ 1 reasonably long, chain-like aggregates are formed which behave like coiling polymer chains with the subunit the Kuhn statistical element. When <s*> > 1 the entire system forms one structure. Data obtained from the literature are analysed. They favor finite size, separate chains. The Kuhn statistical element length, derived from the data, is shown to agree well with the lectin model hypothesis.