The 22 kDa component of the protein complex on the surface of Plasmodium falciparum merozoites is derived from a larger precursor, merozoite surface protein 7

The gene coding for merozoite surface protein 7 has been identified and seq uenced in three lines of Plasmodium falciparum. The gene encodes a 351 amin o acid polypeptide that is the precursor of a 22-kDa protein (MSP7(22)) on the merozoite surface and non-covalently associated with merozoite surface protein 1 (MSP1) complex shed from the surface at erythrocyte invasion. A s econd 19-kDa component of the complex (MSP7(19)) was shown to be derived fr om MSP7(22) and the complete primary structure of this polypeptide was conf irmed by mass spectrometry. The protein sequence contains several predicted helical and two beta elements, but has no similarity with sequences outsid e the Plasmodium databases. Four sites of sequence variation were identifie d in MSP7, all within the MSP7(22) region. The MSP7 gene is expressed in ma ture schizonts, at the same time as other merozoite surface protein genes. It is proposed that MSP7(22) is the result of cleavage by a protease that m ay also cleave MSP1 and MSP6. A related gene was identified and cloned from the rodent malaria parasite, Plasmodium yoelii YM; at the amino acid level this sequence was 23% identical and 50% similar to that of P. falciparum M SP7. (C) 2001 Elsevier Science B.V. All rights reserved.