Bin2, a functionally nonredundant member of the BAR adaptor gene family.

BAR family proteins are a unique class of adaptor proteins characterized by a common N-terminal fold of undetermined function termed the BAR domain. This set of adaptors, which includes the mammalian proteins amphiphysin and Bin1 and the yeast proteins Rvs167p and Rvs161p, has been implicated in diverse cellular processes, including synaptic vesicle endocytosis, actin regulation, differentiation, cell survival, and tumorigenesis. Here we report the identification and characterization of Bin2, a novel protein that contains a BAR domain but that is otherwise structurally dissimilar to other members of the BAR adaptor family. The Bin2 gene is located at chromosome 4q22.1 and is expressed predominantly in hematopoietic cells. Bin2 is upregulated during differentiation of granulocytes, suggesting that it functions in that lineage. Bin2 formed a stable complex in cells with Bin1, but not with amphiphysin, in a BAR domain-dependent manner. This finding indicates that BAR domains have specific preferences for interaction. However, Bin2 did not influence endocytosis in the same manner as brain-specific splice isoforms of Bin1, nor did it exhibit the tumor suppressor properties inherent to ubiquitous splice isoforms of Bin1. Thus, Bin2 appears to encode a nonredundant function in the BAR adaptor gene family.