SS33410, an inhibitor of V-ATPase, blocks intracellular protein transport of the VSV-G protein in the Golgi compartment

An earlier report suggested that SS33410, structurally related to folimycin and bafilomycin A(1), blocked secretion of the glycoprotein (G protein) of vesicular stomatitis virus (VSV) into the medium and, instead, G protein was accumulated intracellulary. To identify the inhibition site of SS33410 in intracellular protein transport, I have analyzed the oligosaccharide chain structure of the intracellularly accumulated G protein. In SS33410-treated VSV-infected cells, G protein oligosaccharide was suggested to have a composition of GlcNAc-Man(5)-GlcNAc(2) as analyzed by Bio-Gel P-4 column chromatography following digestion with alpha-mannosidase, beta-N-acetylhexosaminidase, and then with alpha-mannosidase. SS33410 specifically inhibited vacuolar-type ATPase (V-ATPase). These studies thus suggest that SS33410 blocks the intracellular protein transport before the step of trimming by mannosidase II, which is confined to the medial Golgi compartment.