TBC1 domain family member 9B (TBC1D9B)

TBC1 domain family member 9B (TBC1D9B) is a large (~140 kDa) protein with two N-terminal GRAM domains, a central TBC domain, and a C-terminal EF hand motif[1]. It functions primarily as a GTPase-activating protein for Rab11a, modulating its activity to regulate membrane trafficking—specifically the transcytosis of immunoglobulin A (IgA) in polarized epithelial cells[1][2]. TBC1D9B is also implicated in autophagic flux regulation, interacting with LC3B on autophagosome membranes and potentially ensuring proper autophagosome trafficking and degradation[3]. Although it can interact with additional Rabs (Rab11b, Rab4a, and under certain magnesium conditions, Rab8a), its GAP activity is most pronounced for Rab11a[1][2]. TBC1D9B is not currently considered a direct therapeutic target, nor are there drugs or biomarker applications described in the literature or clinical practice[5][6]. Its biological relevance stems from regulation of protein trafficking and autophagy, and dysfunction may theoretically contribute to cellular transport disorders, but direct disease links have not been established[3][5].

Other names

KIAA0676GRAMD9BTBC1 domain family member 9B (with GRAM domain)TBC1D9B