Sugar digestion in mosquitoes: Identification and characterization of three midgut α-glucosidases of the neo-tropical malaria vector Anopheles aquasalis (Diptera: Culicidae)

Dietary carbohydrates provide an important source of energy for flight, and contribute to longevity and fecundity of mosquitoes. The most common sugar mosquitoes ingest is sucrose, and digestion of this substance is carried out mainly by α-glucosidases. In the current work, we tested the efficiency of sucrose on Anopheles aquasalis female diet. The best longevity (days) was reached when sugar was available in the diet, whereas most only blood fed females were dead 6 days after emergence. Three α-glucosidase isoforms were detected in the adult female midgut, named αGlu1, αGlu2 and αGlu3. These are acidic α-glucosidases with optima pH around pH 5.5. αGlu1 and αGlu2 are present in both secreted and membrane-bound forms, whereas α-Glu3 only in anchored to membranes. The α-glucosidase activity is concentrated mainly in the posterior midgut (70%), both in non-fed or 10% sucrose fed females. The single form of these α-glucosidases seemed to be ∼ 70 kDa polypeptides, although αGlu2 is presented in ≥ 600 kDa self-aggregates. Km values of αGlu1, αGlu2 and αGlu3 differed significantly from each other, supporting the statement that three α-glucosidases are produced in the female midgut. Together, all data suggest that sugar is an essential component of A. aquasalis female diet. In addition, α-glucosidases are synthesized in the same place where sucrose is digested and absorbed, the midgut.