Expression and characterisation of Plasmodium falciparum acidic basic repeat antigen expressed in Escherichia coli

The acidic basic repeat antigen (ABRA) of Plasmodium falciparum has been lo calised on the merozoite surface and in the parasitophorous vacuole. It is one of the antigens enriched in the clusters of merozoites formed with grow th inhibitory immune serum and possesses chymotrypsin-like activity. Chymos tatin, an inhibitor of chymotrypsin, inhibits malaria invasion as well as a utoproteolysis of ABRA. Based on these characteristics of ABRA, it seems im portant for invasion and should be investigated as a target for vaccine and drug design. For the functional characterisation of this protein, the full -length mature ABRA protein and its fragments with/without the putative pro tease active site were cloned, expressed and purified from Escherichia coli . The polyclonal serum raised against recombinant ABRA fragment recognised a parasite protein with a mobility of 101 kDa in an immunoblot assay and sh owed immunofluorescence activity with a schizont-rich preparation of P. fal ciparum. Using a partially purified fragment containing the putative active site and fluorogenic and chromogenic substrates, we established that the p rotease activity of ABRA resides in the N-terminal portion of the protein a nd the highly charged C-terminal part of the protein is not required for th is activity. The protease activity of ABRA was inhibited with serine protea se inhibitors like chymostatin and phenyl methyl sulfonyl fluoride (PMSF) w hereas leupeptin was not able to inhibit this enzyme activity. These result s clearly indicated that ABRA is a protease with chymotrypsin-like specific ity. This is the first report describing the expression and characterisatio n of recombinant ABRA protein. (C) 2000 Elsevier Science B.V. All rights re served.