Pep7p provides a novel protein that functions in vesicle-mediated transport between the yeast Golgi and endosome.
Saccharomyces cerevisiae pep7 mutants are defective in transport of soluble vacuolar hydrolases to the lysosome-like vacuole. PEP7 is a nonessential gene that encodes a hydrophilic protein of 515 amino acids. A cysteine-rich tripartite motif in the N-terminal half of the polypeptide shows striking similarity to sequences found in many other eukaryotic proteins. Several of these proteins are thought to function in the vacuolar/lysosomal pathway. Mutations that change highly conserved cysteine residues in this motif lead to a loss of Pep7p function. Kinetic studies demonstrate that Pep7p function is required for the transport of the Golgi-precursors of the soluble hydrolases carboxypeptidase Y, proteinase A, and proteinase B to the endosome. Integral membrane hydrolase alkaline phosphatase is transported to the vacuole by a parallel intracellular pathway that does not require Pep7p function. pep7 mutants accumulate a 40-60-nm vesicle population, suggesting that Pep7p functions in a vesicle consumption step in vesicle-mediated transport of soluble hydrolases to the endosome. Whereas pep7 mutants demonstrate no defects in endocytic uptake at the plasma membrane, the mutants demonstrate defects in transport of receptor-mediated macromolecules through the endocytic pathway. Localization studies indicate that Pep7p is found both as a soluble cytoplasmic protein and associated with particulate fractions. We conclude that Pep7p functions as a novel regulator of vesicle docking and/or fusion at the endosome.
Webb
G C
GC
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Zhang
J
J
Garlow
S J
SJ
Wesp
A
A
Riezman
H
H
Jones
E W
EW
D048868:Adaptor Proteins, Signal Transducing; D000469:Alkaline Phosphatase / Q000378:metabolism; D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002413:Cations, Divalent; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism; D003598:Cytoskeletal Proteins; D004271:DNA, Fungal; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D006867:Hydrolases / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D011817:Rabbits; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D012995:Solubility; D013696:Temperature; D033921:Vesicular Transport Proteins
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D002413:Cations, Divalent; D003598:Cytoskeletal Proteins; D004271:DNA, Fungal; D005656:Fungal Proteins; C106978:PEP7 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D006867:Hydrolases; D000469:Alkaline Phosphatase