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General Comment |
The human MAT8
cDNA, also symbolized PLML and FXYD3, encodes a deduced 67-amino acid protein with a calculated mass of 8 kD
and shows partial homology to phospholemman (PLM; 602359), a major plasmalemmal substrate for cAMP-dependent
protein kinase and protein kinase C. PLML contains a putative 20-amino acid leader sequence and a putative
transmembrane domain. It shares homologous extracellular and transmembrane domains with PLM, but has 2 cysteine
residues in the transmembrane domain. Unlike PLM, it contains no consensus phosphorylation sites in the cytoplasmic
domain. RNA blot analysis revealed expression of PLML as a major 0.5-kb transcript and minor 2.5- and 3.0-kb
transcripts in all 16 primary human breast tumors and in 8 of 11 human breast carcinoma cell lines studied. Mouse Mat8
is expressed at high levels in the SMF cell line, uterus, stomach, and colon, and at lower levels in breast, ovary, lung,
small intestine, and thymus. Expression of PLML in Xenopus oocytes induces hyperpolarization-activated chloride
currents similar to those induced by PLM expression.
NCBI Summary:
This gene encodes a member of a family of small membrane proteins that share a 35-amino acid signature sequence domain, beginning with the sequence PFXYD and containing 7 invariant and 6 highly conserved amino acids. The approved human gene nomenclature for the family is FXYD-domain containing ion transport regulator. Mouse FXYD5 has been termed RIC (Related to Ion Channel). FXYD2, also known as the gamma subunit of the Na,K-ATPase, regulates the properties of that enzyme. FXYD1 (phospholemman), FXYD2 (gamma), FXYD3 (MAT-8), FXYD4 (CHIF), and FXYD5 (RIC) have been shown to induce channel activity in experimental expression systems. Transmembrane topology has been established for two family members (FXYD1 and FXYD2), with the N-terminus extracellular and the C-terminus on the cytoplasmic side of the membrane. The protein encoded by this gene may function as a chloride channel or as a chloride channel regulator. Two transcript variants encode two different isoforms of the protein; in addition, transcripts utilizing alternative polyA signals have been described in the literature.
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