Functions as guanine nucleotide exchange factor (GEF) with specificity for RAB11A and RAB25 (By similarity). Inhibits the auto- and transphosphorylation activity of BTK. Plays a negative regulatory role in BTK-related cytoplasmic signaling in B-cells. May be involved in BCR-induced apoptotic cell death. Interacts with BTK (By similarity). Interacts with all isoforms of MAPK8, MAPK9, MAPK10 and MAPK12 (By similarity). Interacts with GDP-bound and nucleotide-free forms of RAB11A (PubMed:26506309). Colocalizes with RAB11A on cytoplasmic vesicle membranes. The N-terminal half of the protein mediates interaction with RAB11A and functions as guanine nucleotide exchange factor. Four long alpha-helices (interrupted by a central kink) assemble into coiled coils, giving rise to a 'V' shape. Belongs to the SH3BP5 family.