Functional expression of secreted mouse BST-1 in yeast

BST-1, a bone marrow stromal cell surface antigen, is a glycosyl phosphotidylinositol-anchored protein that stimulates pre-B-cell growth and has adenosine diphosphate (ADP)-ribosyl cyclase and cyclic ADP-ribose (cADPR) hydrolase activity. The two enzymatic activities are responsible for the synthesis and hydrolysis of cADPR, a novel second messenger of calcium release from intracellular calcium stores. The expression and characterization of human BST-1 in certain mammalian cell lines have been reported. We have expressed the murine BST-1 in yeast as a 6 x His-tagged secreted protein. The recombinant protein has been purified and subjected to structural and functional characterization. It has an apparent molecular mass of 38.5 kDa on SDS-PAGE gel stained with Coomassie blue and is recognized on Western blots by a rabbit polyclonal antibody against BST-1. Deglycosylation of the protein with N-glycanase produces a ladder of bands with molecular sizes ranging from 32 to 39 kDa. The protein possesses the ADP-ribosyl cyclase activity as measured using nicotinamide guanine dinucleotide as substrate.