J. Biol. Chem., Vol. 265, Issue 13, 7440-7448, 05, 1990
Biogenesis of vacuolar membrane glycoproteins of yeast Saccharomyces cerevisiae
S Nishikawa, N Umemoto, Y Ohsumi, A Nakano and Y Anraku
Department of Biology, Faculty of Science, University of Tokyo, Japan.
To investigate the biogenesis of the yeast vacuole, we have sought novel
marker proteins localized to the vacuolar membrane. Glycoproteins were
prepared from vacuolar membrane vesicles by concanavalin A- Sepharose
column chromatography and used to raise monoclonal antibodies. The
antibodies obtained recognize several vacuolar proteins that have N-linked
oligosaccharide chains. A set of the antibodies reacts with a vacuolar
glycoprotein with a major molecular species of 72 kDa (vgp72), which
appears to associate peripherally with the vacuolar membrane. The
biosynthesis of vgp72 has been examined in detail by pulse-chase
experiments and by analyses using various secretory mutants (sec18, sec7,
and sec1) and a vacuolar protease mutant (pep4). vgp72 first appears in the
endoplasmic reticulum as a 74- kDa species and is quickly modified in the
Golgi apparatus to two distinct species: a 79-kDa form, and a
heterogeneously glycosylated form (90-150 kDa). Subsequently, both species
are proteolytically processed in the vacuole giving rise to a 72-kDa
species as well as heavily glycosylated form. Thus, the biogenesis of vgp72
utilizes the early part of the secretory pathway as is the case of vacuolar
soluble enzymes. A unique feature is that two species that are different in
the extent of glycosylation appear to follow the same destination to the
vacuolar membrane.