Plasmodium falciparum MAEBL is a unique member of the ebl family

Malaria is one of the deadliest human diseases and efforts to control it have been difficult due to the protozoan parasites' complex biology. Malaria nicrozoite invasion of erythrocytes is an essential part of blood-stage infections. The invasion process is mediated by numerous parasite molecules, such as EBA-175, a member of the ebl family of erythrocyte binding proteins. We have identified maebl. an ebl paralogue, in Plasmodium falciparum and found it highly conserved with its orthologues in P. yoehi and P. berghei, but distinct from other Plasmodium ebl. Importantly, the putative MAEBL ligand domains are highly conserved and are similar to AMA-1, but not the consensus DBL ligand domains present in all other ebl. In Mature merozoites, MAEBL localized with rhoptry proteins (RhopH2. RAP-1). including Surface localization with RhopH2, but not microneme proteins (EBA-175. BAEBL). MAEBL appears as proteoytically processed fragments in P. falciparum parasites. The amino cysteine-rich ligand domains were present primarily in culture supernatants, while the carboxyl cysteine-rich domain adjacent to the transmembrane domain was preferentially isolated from Triton X-100 extracted fractions. These data indicate (hat the primary structure of maebl is highly conserved among Plasmodium species, while its characteristics demonstrate a function unique among the cbl proteins. (C) 2002 Elsevier Science B.V. All rights reserved.