Characterization of an acyl-coenzyme A binding protein predominantly expressed in human primitive progenitor cells.

Human acyl-coenzyme A binding domain-containing member 6 (ACBD6) is a modular protein that carries an acyl-CoA binding domain at its N terminus and two ankyrin motifs at its C terminus. ACBD6 binds long-chain acyl-CoAs with a strong preference for unsaturated, C18:1-CoA and C20:4-CoA, over saturated, C16:0-CoA, acyl species. Deletion of the C terminus, which is not conserved among the members of this family, did not affect the binding capacity or the substrate specificity of the protein. ACBD6 is not a ubiquitous protein, and its expression is restricted to tissues and progenitor cells with functions in blood and vessel development. ACBD6 was detected in bone marrow, spleen, placenta, cord blood, circulating CD34+ progenitors, and embryonic-like stem cells derived from placenta. In placenta, the protein was only detected in CD34+ progenitor cells present in blood and in CD31+ endothelial cells surrounding the blood vessels. These cells were also positive for the marker CD133, and they probably constitute hemangiogenic stem cells, precursors of both blood and vessels. We propose that human ACBD6 represents a cellular marker for primitive progenitor cells with functions in hematopoiesis and vascular endothelium development.