A Novel RING Finger Protein, Vps8p, Functionally Interacts with the Small GTPase, Vps21p, to Facilitate Soluble Vacuolar Protein Localization

• Published in: The Journal of biological chemistry 1996-12, Vol.271 (52), p.33607-33615
• Main Authors: Horazdovsky, Bruce F., Cowles, Christopher R., Mustol, Peg, Holmes, Michael, Emr, Scott D.
• Format: Article
• Language: English
• Subjects: Alkaline Phosphatase - metabolism; Amino Acid Sequence; BIOCHIMIE; BIOQUIMICA; Carrier Proteins - chemistry; Carrier Proteins - metabolism; COMPOSICION QUIMICA; COMPOSITION CHIMIQUE; Electrophoresis, Polyacrylamide Gel; FOSFATASA ALCALINA; Fungal Proteins - metabolism; GENE; GENES; GTP Phosphohydrolases - metabolism; GTP-Binding Proteins - metabolism; HIDROLASAS; HYDROLASE; MEMBRANAS CELULARES; MEMBRANE CELLULAIRE; METABOLISME DES PROTEINES; METABOLISMO PROTEICO; Molecular Sequence Data; MUTANT; MUTANTES; PEPTIDASAS; PEPTIDASE; PHOSPHATASE ALCALINE; PROTEINAS AGLUTINANTES; PROTEINE DE LIAISON; rab GTP-Binding Proteins; Restriction Mapping; SACCHAROMYCES CEREVISIAE; Saccharomyces cerevisiae Proteins; SECUENCIA NUCLEOTIDICA; SEQUENCE NUCLEOTIDIQUE; Subcellular Fractions - chemistry; VACUOLA; VACUOLE; Vesicular Transport Proteins
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.271.52.33607

Genetic analyses of vacuolar protein sorting in Saccharomyces cerevisiae have uncovered a large number of mutants (vps) that missort and secrete soluble vacuolar hydrolases. Here we report the characterization of the gene product affected in one of these mutants, Vps8p. Polyclonal antiserum raised against a trpE-Vps8 fusion protein specifically detects a 134-kDa protein in labeled yeast cell extracts. Subcellular fractionation studies demonstrate that Vps8p is distributed between a low speed membrane pellet fraction and a high speed membrane pellet fraction. The lack of a hydrophobic domain in Vps8p suggests that Vps8p peripherally associates with a membrane(s). This association was found to depend on the function of Vps21p, a member of the Rab/Ypt/Sec4 family of small GTPases. In vps21 null mutant cells, Vps8p is found in the cytosol. In addition, overexpression of Vps21p partially suppresses a vps8 null mutant, indicating that Vps8p and Vps21p functionally interact. Vps8p contains a C-terminal cysteine-rich region that conforms to the H2 variant of the RING finger Zn2+ binding motif. Truncation of this C-terminal region partially compromises Vps8p function. While vps8 null mutant strains missort and secrete soluble vacuolar hydrolases, the integral vacuolar membrane protein, alkaline phosphatase (ALP), is sorted to the vacuole and matured normally. In addition, when vps8 mutants are combined with endocytic or late secretory pathway mutants (end3 or sec1, respectively), ALP is still delivered to the vacuole. These observations indicate that ALP is sorted to the vacuole in a Vps8p-independent manner, possibly via an alternative vesicle carrier.