Bestrophin is a 68-kDa basolateral plasma membrane protein expressed in retinal pigment epithelial cells (RPE). It is encoded by the VMD2 gene, which is mutated in Best macular dystrophy, a disease characterised by a depressed light peak in the electrooculogram [1]. VMD2 encodes a 585-amino acid protein with an approximate mass of 68 kDa which has been designated bestrophin. Bestrophin shares homology with the Caenorhabditis elegans RFP gene family, named for the presence of a conserved arginine (R), phenylalanine (F), proline (P), amino acid sequence motif. Bestrophin is a plasma membrane protein, localised to the basolateral surface of RPE cells consistent with a role for bestrophin in the generation or regulation of the EOG light peak. Bestrophin and other RFP family members represent a new class of chloride channels, indicating a direct role for bestrophin in generating the light peak [1]. The VMD2 gene underlying Best disease was shown to represent the first human member of the RFP-TM protein family. More than 97% of the disease-causing mutations are located in the N-terminal RFP-TM domain implying important functional properties [2]. The bestrophins are four-pass transmembrane chloride-channel proteins [3], and the RFP-TM or bestrophin domain extends from the N-terminus through approximately 350 amino acids and contains all of the TM domains as well as nearly all reported disease causing mutations [4]. Interestingly, the RFP motif is not conserved evolutionarily back beyond Metazoa, neither is it in plant members.

1: Bestrophin interacts physically and functionally with protein phosphatase 2A. Marmorstein LY, McLaughlin PJ, Stanton JB, Yan L, Crabb JW, Marmorstein AD; J Biol Chem 2002;277:30591-30597. PMID:12058047

2: Three novel human VMD2-like genes are members of the evolutionary highly conserved RFP-TM family. Stohr H, Marquardt A, Nanda I, Schmid M, Weber BH; Eur J Hum Genet 2002;10:281-284. PMID:12032738

3: Structure-function analysis of the bestrophin family of anion channels. Tsunenari T, Sun H, Williams J, Cahill H, Smallwood P, Yau KW, Nathans J; J Biol Chem. 2003;278:41114-41125. PMID:12907679

4: Functional roles of bestrophins in ocular epithelia. Marmorstein AD, Cross HE, Peachey NS; Prog Retin Eye Res. 2009;28:206-226. PMID:19398034