The following vertebrate small integral membrane glycoproteins are
evolutionary related [1,2,3]:
Peripheral myelin protein 22 (PMP-22), which is expressed in many tissues
but mainly by Schwann cells as a component of myelin of the peripheral
nervous system (PNS). PMP-22 probably plays a role both in myelinization
and in cell proliferation. Mutations affecting PMP-22 are associated with
hereditary motor and sensory neuropathies such as Charcot-Marie-Tooth
disease type 1A (CMT-1A) in human or the 'trembler' phenotype in mice.
Eye lens specific membrane protein 20 (MP20 or MP19).
Epithelial membrane protein-1 (EMP-1) (also kwown as tumor-associated
membrane protein (TMP) or as squamous cell-specific protein Cl-20).
Epithelial membrane protein-2 (EMP-2) (also kwown as XMP).
Epithelial membrane protein-3 (EMP-3) (also kwown as YMP).
These are proteins of about 160 to 173 amino acid residues that contain four
transmembrane segments. PMP-22, EMP-1, -2 and -3 are highly similar, while
MP20 is more distantly related.
We selected two conserved regions as signature patterns, the first pattern
includes the end of the first transmembrane region and part of the loop before
the second region. The second pattern corresponds to the third transmembrane
The PMP-22 family is evolutionary related to the claudin family (see
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