Range of the influence of the carbohydrate moiety on the conformation of the poly(amino acid) backbone in glycosylated mucins.

The influence of glycosylation on the conformational properties of porcine submaxillary gland mucin has been investigated using rotational isomeric state theory. The specific objective was to determine the conditions under which the polypeptide has the relatively large mean square unperturbed radius of gyration mean value of s2(0), demanded by the measurements of Shogren et al., while retaining the overall architecture of a random coil. The mean square dimensions were monitored as the dimensionless characteristic ratio defined as C = mean value of s2(0)/npl2p, and the overall architecture was monitored by another dimensionless ratio mean value of r2(0)/mean value of s2(0), where mean value of r2(0) denotes the mean square unperturbed end-to-end distance. The computed values of C cannot reproduce the measured values if the conformational influence of glycosylation is restricted to each Ser or Thr, or if this influence extends only as far as their nearest neighbors. Values of C compatible with experiment can be obtained if the influence extends to next nearest neighbors. The behavior of the computed values of mean value of r2(0)/mean value of s2(0) permits an assignment of 7 +/- 1 as the likely upper limit to the number of consecutive amino acid residues that experience alterations in phi and psi if the sequence contains a glycosylated Ser or Thr.