Characterization of Female Specific Salivary Gland Glycoproteins of Anopheles Gambiae and their Interaction with Plasmodium Berghei Sporozoites
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This study investigated the female specific salivary gland glycoproteins of Anopheles gambiae mosquitoes and their possible role in malaria sporozoite invasion of the salivary glands. Male and female Anopheles gambiae salivary gland proteins were analyzed by western blot with various lectins to identify glycoproteins that are specific to the female salivary glands. At least, 14 female glycoproteins were detected by specific lectins in the female glands but not in the male glands and were designated as female specific. The different morphological regions of the female salivary glands showed distinct lectin binding characteristics with the distal lateral and the median regions displaying the most glycoproteins. The lectins that identified the most female specific glycoproteins were tested in a transplantation assay to determine their effect on Plasmodium berghei sporozoite invasion of the salivary glands. The transplantation procedure was similar to that reported by Rosenberg (1985) with some improvements which resulted in 90-95% mosquito survival after the transplant procedure. Up to 3% of the total sporozoites that invaded the salivary glands were found in the transplanted glands. The results of our analyses showed that the lectins soybean agglutinin (SBA) and wheat germ agglutinin (WGA) significantly reduced sporozoite invasion while the lectins Concanavalin agglutinin (Con A) and Dolichos biflorus agglutinin (DBA) had no effect on sporozoite invasion. The pattern of distribution of glycoconjugates on the female salivary glands showed that Con A bound uniformly and moderately to the whole gland while SBA and WGA bound intensely to the distal ends of the median and lateral lobes of the salivary glands. The binding pattern of SBA and WGA corresponds to the regions of the female glands where sporozoites enter the glands. These results suggest that malaria sporozoites interact with specific carbohydrate molecules on the salivary glands for invasion. To characterize salivary gland surface glycoproteins that may be involved in sporozoite invasion, salivary gland surface proteins were labeled by the biotinylation reagent sulfosuccinimidyl 6-biotinamido hexanoate, followed by lectin affinity chromatography. 7 of the labeled surface glycoproteins detected by sporozoite blocking lectins (SBA and WGA) had molecular weights corresponding to female specific glycoproteins. These female specific salivary gland surface glycoproteins are of potential interest in studying sporozoite interaction with salivary gland glycoconjugates. To determine that malaria sporozoites capable of invading mosquito salivary glands interact with carbohydrate molecules, hemagglutination and carbohydrate binding assays were conducted using sporozoites isolated from infected mosquito midguts. The results obtained suggest that interaction of sporozoites with mosquito salivary gland glycoconjugates may be mediated by sporozoite proteins other than the circumsporozoite protein, the major protein covering the surface of sporozoites.