Molecular Basis for Genetic Resistance of Anopheles gambiae to Plasmodium: Structural Analysis of TEP1 Susceptible and Resistant Alleles

Abstract

Thioester-containing protein 1 (TEP1) is a central component in the innate immune response of Anopheles gambiae to Plasmodium infection. Two classes of TEP1 alleles, TEP1*S and TEP1*R, are found in both laboratory strains and wild isolates, related by a greater or lesser susceptibility, respectively to both P. berghei and P. falciparum infection. We report the crystal structure of the full-length TEP1*S1 allele which, while similar to the previously determined structure of full-length TEP1*R1, displays flexibility in the N-terminal fragment comprising domains MG1-MG6. Amino acid differences between TEP1*R1 and TEP1*S1 are localized to the TED-MG8 domain interface that protects the thioester bond from hydrolysis and structural changes are apparent at this interface. As a consequence cleaved TEP1*S1 (TEP1*S1cut) is significantly more susceptible to hydrolysis of its intramolecular thioester bond than TEP1*R1cut. TEP1*S1cut is stabilized in solution by the heterodimeric LRIM1/APL1C complex, which preserves the thioester bond within TEP1*S1cut. These results suggest a mechanism by which selective pressure on the TEP1 gene results in functional variation that may influence the vector competence of A. gambiae towards Plasmodium infection.

The structure and function of thioester-containing proteins in arthropods

“…Ag TEP1 is a key factor in the immune response of mosquitoes to malaria, binding to Plasmodium ookinetes in the basal lamina of the midgut epithelium and targeting them for lysis (Blandin et al 2004; Fraiture et al 2009; Povelones et al 2009, 2011; Baxter et al 2010; Le et al 2012). Unlike complement C3 or A 2 M, Ag TEP1 is secreted as a full-length protein but is cleaved within the protease-sensitive region to produce a two-chain molecule Ag TEP1 cut .…”

Structure of a bacterial α2-macroglobulin reveals mimicry of eukaryotic innate immunity

“…In addition, electron microscopy structures have provided some insight into the conformational change undergone by eukaryotic A2M in the protease-trapping process 10,19,20 , but there are no crystal structures of A2M in the native or protease-activated forms. Insight into the mechanism of target protease trapping has been obtained from crystal structures of components of the complement system and mosquito TEP1, which provide details about the architecture of the A2M/ complement/TEP superfamily and the domain rearrangements that are required for the activation of these proteins 17,[21][22][23][24][25][26][27] , but these details remain specific to proteins involved in complement activation. Thus, despite the central importance of A2Ms in innate immunity, detailed structural characterization of an A2M is still lacking.…”

Arthropod Innate Immune Systems and Vector-Borne Diseases

“…72 Cleavage of TEP1 in the protease-sensitive region produces TEP1 cut , which requires the LRIM1/APL1C heterodimer for stability both in vitro and in vivo . 73,74 …”