Ion-exchange-immunoaffinity purification of a recombinant baculovirus Plasmodium falciparum apical membrane antigen, PF83/AMA-1.

A two-step purification regime has been developed for a quantitatively minor, putatively transmembrane, M(r) 83,000, apical membrane blood stage vaccine candidate antigen of Plasmodium falciparum (PF83/AMA-1), that has been expressed as a full-length baculovirus recombinant protein, PF83-7G8-1. The first step utilizes a new approach to high-performance ion-exchange chromatography (HPIEC) in which elution conditions are not only defined by charge, but also by hydrophobicity. HPIEC fractionation involves successive sodium chloride gradient anion-exchange elutions (A and B), where a change in the non-ionic detergent polyoxyethylenealkylether C10E5 concentration between elutions A and B (from 0.01% to 0.1% (w/v) respectively), results in a fraction that comprises from 2% to 9% PF83-7G8-1. Subsequent column immunoaffinity purification of this fraction on Q-Sepharose CL 4B-28G2dc1 mAb yields a PF83-7G8-1 preparation that is 56% pure. Rat mAb 28G2dc1 recognizes a C-terminal region that is conserved and cross reactive within the AMA-1 family, thus permitting recombinant and native full-length AMA-1 molecules from other species to be purified for molecular analysis. Immunological and molecular characterisation of the vaccine-related characteristics of purified PF83/AMA-1 are now underway.