CDNA-BASED FUNCTIONAL DOMAINS OF A CALNEXIN-LIKE MELANOSOMAL PROTEIN,P90

We have recently identified a gene encoding a calnexin-like protein (p 90) by the immunoscreening of a human melanoma cDNA library, using a r abbit anti-human melanosomal antibody. This p90 protein was highly exp ressed by human melanocytes and associated with melanosomal membrane a nd endoplasmic reticulum. In this study we report the computer analysi s of the predicted amino acid sequence of this calnexin-like melanosom al protein. We found that p90 is a membrane-bound protein whose large N-terminal domain is located within the melanosomal compartment; its s horter C-terminal is exposed to the cytosol and separated by a short t ransmembrane region. This p90 protein was found to have consensus sequ ences of a Ca2+-binding loop and a protein kinase C phosphorylation si te at the N-terminal domain. The C-terminal domain, on the other hand, contained sequences of a casein kinase II phosphorylation site and tw o protein kinase A phosphorylation sites. Such functional motifs could provide signal transduction across the melanosomal membrane, the rece ption of melanogenic protein vis carriers at the melanosomal membrane and the translocation of melanosomes in the melanocyte.