Isolation and characterization of a novel four-transmembrane protein PMP22CD specifically expressed in the testis

PMP22_ Claudin family proteins play important roles in cell tight junction. In this study, we have identified a novel member of this family, PMP22CD. Human PMP22CD was first discovered by database sequence mining and analysis, and verified by cloning and sequencing. PMP22CD was isolated from the human testis cDNA library and mapped to chromosome 11q24.1 by browsing the UCSC genomic database. It contains an ORF with a length of 675bp, encoding a protein that contains a putative PMP22_ Claudin domain with four transmembrane helices. Its molecular weight and isoelectric point are predicted to be 25.8kDa and 8.42, respectively. The PMP22CD protein is highly conservative in mammal animals. Phylogenetic tree analysis indicated that PMP22CD stands for a new subgroup in the PMP22/ EMP/ Claudin family. RT-PCR analysis showed that PMP22CD was specifically expressed in the testis. Green fluorescence protein localization analysis showed that PMP22CD mainly surrounded the nuclear membrane, with a minority distribution in the cytoplasm. These results suggested that PMP22CD is a distant member of the PMP22/ EMP/ Claudin family and that it may have a novel function that does not involve cell tight junction because it is not located at the cell membrane.