STRUCTURAL AND FUNCTIONAL STUDIES OF MONKEY SALIVARY MUCIN

Much evidence suggests that mucins play an integral role in the nonimmune protection of the oral cavity. In particular, microbial colonization is thought to be influenced by specific interactions between salivary mucins and bacterial lectins and/or enzymes. As a prelude towards understanding the molecular basis of such interactions, the carbohydrate side chains of monkey salivary mucins were isolated and characterized. Considerable size and charge hetergeneity were noted. The principal oligosaccharide was a neutral pentasaccharide comprising approximately 26% of the total recovered saccharide. Based upon glycosidase digestion, Smith-periodate oxidation and GC/MS analysis of methylated derivatives, the structure of this oligosaccharide may be tentatively written as

Gal(beta)1(--->)4 GlcNAc (beta)1(--->)3 GalNAc

(UPARR) 1(--->)6

Gal

(UPARR) (alpha)1(--->)2

Fuc

In addition to the neutral oligosaccharide, a series of acidic oligosaccharides were examined. In general, the large molecular weight chains were sulfated and displayed more charge heterogeneity than the smaller sialyated species. The anionic character of these oligosaccharides may be attributed to either GlcNac-4-SO(,4) or NeuAc, which in part, may be acylated at C-7, 8 or 9. Insufficient material precluded definitive analysis of the acidic oligosaccharide.

Immunochemical studies indicated that goat antisera raised to the intact, "homogeneous" monkey mucin contained multiple specificity. Reactivity was demonstrable against both complex oligosaccharides and non-glycosylated regions of the molecule. Asialo-mucin precipitated more antibody than control material as determined by quantitative precipitin analysis, suggesting an indirect role for sialic acids in the antigenicity of this molecule.

The interaction of {('3)H} - monkey mucin to Streptococcus sanguis 10556 was examined by the method of isotopic dilution. Only a small percentage of the potential ligand could be demonstrated to bind specifically to these cells, suggesting that the microheterogeneity of mucin may have functional consequence.

It is not clear if the microheterogeneity displayed by mucin glycoproteins is accidental or contrived. Several lines of evidence, however, suggest the latter indicating that the variation in mucin structure may play a regulatory role in the biological functions of these protective macromolecules.