We report functional expression of BCRP in Pichia pastoris in which BCRP was produced as a 62 kDa underglycosylated protein. BCRP expression level in P. pastoris was comparable to that in HEK cells. The basal BCRP ATPase activity in the yeast membranes was approximately 40-80 nmol P-i/min/mg protein, which can be modulated by known BCRP substrates and inhibitors. Photolabeling of BCRP with 8-azido[alpha-P-32]ATP was dependent preferentially on the presence of Co2+ than Mg2+ and could be inhibited by a molar excess of ATP. Vanadate-induced trapping of 8-azido[alpha-P-32]ADP by BCRP was much more significant in the presence of Co2+ than that with Mg2+. The K. and V a, values of BCRP for [H-3]E1S transport were 3.6 +/- 03 muM and 55.2 +/- 1.6 pmol/min/mg protein, respectively. This efficient and cost-effective expression system should facilitate large scale production and purification of BCRP for further structural and functional analyses. (C) 2004 Elsevier Inc. All rights reserved.