A mutation within the transmembrane domain of melanosomal protein Silver (Pmel17) changes lumenal fragment interactions.
Melanocytes synthesize and store melanin within tissue-specific organelles, the melanosomes. Melanin deposition takes place along fibrils found within these organelles and fibril formation is known to depend on trafficking of the membrane glycoprotein Silver/Pmel17. However, correctly targeted, full-length Silver/Pmel17 cannot form fibers. Proteolytic processing in endosomal compartments and the generation of a lumenal Malpha fragment that is incorporated into amyloid-like structures is also essential. Dominant White (DWhite), a mutant form of Silver/Pmel17 first described in chicken, causes disorganized fibers and severe hypopigmentation due to melanocyte death. Surprisingly, the DWhite mutation is an insertion of three amino acids into the transmembrane domain; the DWhite-Malpha fragment is unaffected. To determine the functional importance of the transmembrane domain in organized fibril assembly, we investigated membrane trafficking and multimerization of Silver/Pmel17/DWhite proteins. We demonstrate that the DWhite mutation changes lipid interactions and disulfide bond-mediated associations of lumenal domains. Thus, partitioning into membrane microdomains and effects on conformation explain how the transmembrane region may contribute to the structural integrity of Silver/Pmel17 oligomers or influence toxic, amyloidogenic properties.
Kuliawat
Regina
R
Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA. kuliawat@aecom.yu.edu
Santambrogio
Laura
L
D000595:Amino Acid Sequence; D000818:Animals; D018929:Cell Culture Techniques; D002645:Chickens; D006367:HeLa Cells; D006801:Humans; D008544:Melanocytes / Q000378:metabolism*; D020460:Melanosomes / Q000235:genetics* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D058951:gp100 Melanoma Antigen
D008562:Membrane Glycoproteins; C548637:PMEL protein, human; C548642:Pmel protein, mouse; D058951:gp100 Melanoma Antigen
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