Binds sperm in vitro and promotes sperm capacitation. Specifically promotes capacitation induced by high density lipoproteins (HDLs). Also binds heparin, phospholipid liposomes, and weakly to gelatin. Does not bind chondroitin sulfate B. . This is the function of BSPH1 (binder of sperm protein homolog 1, Ensembl gene identifier ENSG00000188334).