Analysis of adhesive domains from the A4VAR Plasmodium falciparum erythrocyte membrane protein-1 identifies a CD36 binding domain

The A4VAR is a variant antigen expressed by a clonal line that binds CD36 a nd intercellular adhesion molecule-1, ICAM-1. We have cloned and sequenced the extracellular domain coded by the A4var gene. To probe the relationship between A4var expression and parasite adhesion to ICAM-1, var mRNA and pro tein expression were analyzed in an enriched population of A4 parasites tha t displayed higher ICAM-1 binding. By Northern analyses, A4var was the pred ominant var message and antisera raised against a recombinant A4VAR protein reacted with the majority of infected erythrocytes, reinforcing previous c onclusions that A4VAR binds ICAM-1. A4VAR contains five Duffy-binding like (DBL) domains, and two cysteine-rich interdomain regions (CIDR) domains. DB L and CIDR domains from A4VAR were expressed in mammalian cells to determin e which regions mediate binding to CD36 and ICAM-1. Using several different binding assays, the A4VAR CIDR1 was the only domain found to bind CD36. In contrast, the same assays were unable to identify the ICAM-1 binding domai n in A4VAR. This is the first time that each of the DBL and CIDR domains fr om a Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) have bee n systematically expressed and tested for binding. These results confirm th at CIDR1 is sufficient to bind CD36 without any apparent contribution from other domains. (C) 1998 Elsevier Science B.V. AII rights reserved.