question: Which is the protein (antigen) targeted by anti-Vel antibodies in the Vel blood group?
answer: Disruption of SMIM1 causes the Vel- blood type. The protein carrying the Vel blood group antigen was biochemically purified from red blood cell membranes. Mass spectrometry-based de novo peptide sequencing identified this protein to be small integral membrane protein 1 (SMIM1), a previously uncharacterized single-pass membrane protein. Expression of SMIM1 cDNA in Vel- cultured cells generated anti-Vel cell surface reactivity, confirming that SMIM1 encoded the Vel blood group antigen. (PMID: 23505126)