Transmembrane protein 138 (TMEM138)

Transmembrane protein 138 (TMEM138) is a 162-amino acid, four-pass transmembrane protein of about 18.4 kDa, highly conserved among vertebrates and localized primarily to the photoreceptor connecting cilium, which is structurally analogous to the transition zone of primary cilia[1][2][4]. TMEM138 forms part of a membrane complex with Ahi1 and Tmem231 and interacts directly with rhodopsin, facilitating its trafficking between the inner and outer segments of photoreceptor cells, which is essential for normal photoreceptor function and the maintenance of visual capacity[1][2][4]. Loss of TMEM138 disrupts the ciliary complex, mislocalizes rhodopsin, and causes a failure in photoreceptor outer segment morphogenesis, ultimately leading to rapid photoreceptor degeneration and is implicated in ciliopathies including Joubert syndrome (JBTS16)[1][2][4]. TMEM138 is not currently considered a therapeutic drug target, nor are there drugs known to interact with it, but pathogenic variants have clear genetic and mechanistic relevance in inherited retinal and ciliary disorders[3].

Other names

TMEM138HSPC196HSPC198JBTS16