Display of Plasmodium adhesive domains on lambda phages.

Efficient transmission of the malaria parasite by the mosquito vector requires successful invasion of the salivary glands, a process involving specific molecular interactions. Although different studies in the last decade highlighted the possible role of a few sporozoite surface proteins the key players of the invasion process have remained elusive so far. With the objective to improve our understanding of sporozoites-salivary gland interaction, we are using an approach that involves the display on the lambda surface of putative adhesive domains from a few selected Plasmodium proteins possibly implicated in salivary gland recognition/invasion. This collection of lambda phages can be employed for the development of affinity selection experiments targeted to the identification of salivary gland receptors. The lambda system allows the display of relatively large domains (up to 400 aminoacids) and, therefore, it is particularly suitable for our purpose. As a first step toward this direction, adhesive domains from selected P. falciparum and P. berghei surface proteins (such as TRAP, CS, MAEBL, etc) have been fused to the C-terminus of the abundant capsid protein gpD. The different domains were PCR-amplified, cloned in a plasmid vector, sequenced and finally ligated into the lambda vector λD4 (kindly provided by Dr. S. Nasi, CNR, Rome). After packaging, different recombinant lambda clones were randomly isolated from this phage collection and analyzed by western blot to verify the expression of the fusion proteins. All lambda clones identified and isolated so far seem to express recombinant proteins of the expected size. Verification of correct display for all selected domains, as well as binding assays to mosquito salivary glands, is in progress.