Identification of a melanosomal membrane protein encoded by the pink-eyed dilution (type II oculocutaneous albinism) gene.
The pink-eyed dilution (p) locus in the mouse is critical to melanogenesis; mutations in the homologous locus in humans, P, are a cause of type II oculocutaneous albinism. Although a cDNA encoded by the p gene has recently been identified, nothing is known about the protein product of this gene. To characterize the protein encoded by the p gene, we performed immunoblot analysis of extracts of melanocytes cultured from wild-type mice with an antiserum from rabbits immunized with a peptide corresponding to amino acids 285-298 of the predicted protein product of the murine p gene. This antiserum recognized a 110-kDa protein. The protein was absent from extracts of melanocytes cultured from mice with two mutations (pcp and p) in which transcripts of the p gene are absent or greatly reduced. Introduction of the cDNA for the p gene into pcp melanocytes by electroporation resulted in expression of the 3.3-kb mRNA and the 110-kDa protein. Upon subcellular fractionation of cultured melanocytes, the 110-kDa protein was found to be present in melanosomes but absent from the vesicular fraction; phase separation performed with the nonionic detergent Triton X-114 confirmed the predicted hydrophobic nature of the protein. These results demonstrate that the p gene encodes a 110-kDa integral melanosomal membrane protein and establish a framework by which mutations at this locus, which diminish pigmentation, can be analyzed at the cellular and biochemical levels.
Rosemblat
S
S
Ronald O. Perelman Department of Dermatology, New York University School of Medicine, New York 10016.
Durham-Pierre
D
D
Gardner
J M
JM
Nakatsu
Y
Y
Brilliant
M H
MH
Orlow
S J
SJ
D016115:Albinism, Oculocutaneous / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D002352:Carrier Proteins; D002458:Cell Fractionation; D002469:Cell Separation; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018076:DNA, Complementary; D006801:Humans; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism*; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D026901:Membrane Transport Proteins; D051379:Mice; D008817:Mice, Mutant Strains; D008969:Molecular Sequence Data; D014162:Transfection
D002352:Carrier Proteins; D018076:DNA, Complementary; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C489600:OCA2 protein, human; C076239:P protein, mouse