Identification of a transmembrane glycoprotein specific for secretory vesicles of neural and endocrine cells.

TLDR

Secretory vesicles store proteins in many cell types, and it is generally assumed that their molecular machinery is conserved across different cells. The protein was identified by cross‑reactivity of monoclonal antibodies raised against purified cholinergic synaptic vesicles from fish electric organs. We identified a ~100 kDa transmembrane glycoprotein present in secretory vesicles of neurons and endocrine cells from fish to mammals, localized to the cytoplasmic face and shown to be glycosylated, as its mobility shifts to ~62 kDa when synthesized with tunicamycin.

Abstract

Several types of cells store proteins in secretory vesicles from which they are released by an appropriate stimulus. It might be expected that the secretory vesicles in different cell types use similar molecular machinery. Here we describe a transmembrane glycoprotein (Mr approximately 100,000) that is present in secretory vesicles in all neurons and endocrine cells studied, in species from elasmobranch fish to mammals, and in neural and endocrine cell lines. It was detected by cross-reactivity with monoclonal antibodies raised to highly purified cholinergic synaptic vesicles from the electric organ of fish. By immunoprecipitation of intact synaptic vesicles and electron microscopic immunoperoxidase labeling, we have shown that the antigenic determinant is on the cytoplasmic face of the synaptic vesicles. However, the electrophoretic mobility of the antigen synthesized in the presence of tunicamycin is reduced to Mr approximately 62,000, which suggests that the antigen is glycosylated and must therefore span the vesicle membrane.