Transmembrane Protein 55B (TMEM55B)

TMEM55B catalyzes the degradation of phosphatidylinositol 4,5-bisphosphate (PtdIns-4,5-P2) by removing the 4-phosphate. The deduced 257-amino acid protein contains a central Cx(5)R phosphatase catalytic motif and 2 transmembrane domains near its C terminus, a characteristic of lysosomal transmembrane proteins. RNA dot blot analysis detected expression in all tissues examined. Fluorescence-tagged TMEM55B localized with membrane markers of late endosomes or lysosomes. Endogenous HeLa cell TMEM55B showed a similar distribution.It showed no activity toward other phosphatidylinositol substrates or inositol phosphates tested. Overexpression of TMEM55B in human embryonic kidney cells reduced the total cellular level of PtdIns-4,5-P2.