The epithelial membrane proteins (EMP-1, -2 and -3), peripheral myelin protein 22 (PMP22), and lens fibre membrane intrinsic protein (LMIP) comprise a protein family on the basis of sequence and structural similarities []. Each family member is a small hydrophobic membrane glycoprotein, ~160-170 amino acids in length, and shares a common predicted transmembrane (TM) topology of 4 TM domains, with intracellular N- and C-termini [].PMP22, also termed growth-arrest specific protein (GAS3), is a structural component of compact myelin in the peripheral nervous system. Aberrant expression of the PMP22 gene, and mutations in the protein, are associated with a variety of hereditary peripheral motor and sensory neuropathies []. An intra-chromosomal duplication containing the PMP22 gene is found in the majority of patients suffering from the autosomal dominant demyelinating neuropathy Charcot-Marie-Tooth disease 1A (CMT1A) []. In addition, rare point mutations in PMP22 have been found in non-duplication CMT1A patients and in the severe congenital peripheral neuropathy Dejerine-Sottas syndrome [].PMP22 is also implicated in the control of cell proliferation. Its expression levels are up-regulated in cells undergoing growth arrest [], and it has been shown that modulating PMP22 levels in cultured Schwann cells exerts a profound effect on the length of the G1 phase of the cell cycle []. It has also been demonstrated that over-expression of PMP22 in NIH 3T3 fibroblast cells induces apoptosis [].
The 22kDa peroxisomal membrane protein (PMP22) is a major component of peroxisomal membranes. PMP22 seems to be involved in pore-forming activity and may contribute to the unspecific permeability of the organelle membrane. PMP22 is synthesised on free cytosolic ribosomes and then directed to the peroxisome membrane by specific targeting information []. SYM1 in yeast and Mpv17 in higher eukaryotes are closely related peroxisomal proteins required to maintain mitochondrial DNA (mtDNA) integrity and stability [, ]. Mpv17 is involved in the development of early-onset glomerulosclerosis [].Woronin sorting complex protein from Neurospora crassa is also included in this family. It is involved in both Woronin bodies (WB) formation and inherence [].
