Two-dimensional gel analysis of haemolymph proteins from Plasmodium-melanizing and -non-melanizing strains of Anopheles gambiae

Haemolymph polypeptides from Plasmodium-refractory and -susceptible mosquit oes were compared by one- and two-dimensional gel electrophoresis. The refr actory strain of Anopheles gambiae kills malaria parasites by a humoral mel anization mechanism whereas the parasites develop normally in susceptible m osquitoes. The two strains respond in a similar manner to carboxy-methyl-Se phadex beads that have been injected into the thoracic haemocoel, i.e. bead s are strongly melanized in refractory but not susceptible mosquitoes. Prot ein profiles were compared between strains following cold shock (naive cont rol), saline injection and Sephadex bead injection. Using the susceptible n aive control as the standard, eight constitutively expressed polypeptides w ere specific to naive susceptible mosquitoes while twelve other spots were reduced, enhanced or specific to refractory mosquitoes. Several of the stra in-specific spots probably comprise related pairs (one in each strain) whic h vary only in isoelectric focusing point. Nine spots were induced by sham injection or by an injection of beads or saline, but none was reproducibly different between the strains. Amino acid sequence analysis of one of the r efractory strain-specific spots identified it as AgSp14D1, an A. gambiae in fection-responsive serine protease that is most similar to the Drosophila g ene easter and Manduca prophenoloxidase activating enzyme. This gene maps t o polytene chromosome division 14, which has been implicated in the melaniz ation phenotype by quantitative trait loci mapping.