Identification of organ-specific glycosylation of a membrane protein in two tissues using lectins.

Since glycosylation of proteins is performed by the host cell, and variable sugar groupings can confer heterogeneity on the same polypeptide, we wished to see whether membrane proteins, in particular the ubiquitous transmembrane Na,K-ATPase, could be glycosylated differently in different organs. Using a highly sensitive enzyme-linked antibody detection system of bound digoxigenin-labelled lectins on nitrocellulose sheets containing electroblotted alpha and beta subunits of kidney and brain Na,K-ATPase, isolated from various rat strains, in combination with isoform-specific immunoblots, we discovered that brain Na,K-ATPase was highly mannosylated in contrast to renal Na,K-ATPase. Thus, we describe the existence of organ-related glycoforms of an integral ubiquitous membrane protein, i.e. diversification of the same polypeptide by organ-typical sugars. At the same time, the presence of the same glycosylation pattern can make distinct protein isoforms occurring in a same organ more homogeneous. Such organ-related glycoforms may serve for tissue identification and as tissue-specific receptors.