Structural and functional comparisons of salivary α-glucosidases from the mosquito vectors Aedes aegypti, Anopheles gambiae, and Culex quinquefasciatus.

Mosquito vectors of medical importance both blood and sugar feed, and their saliva contains bioactive molecules that aid in both processes. Although it has been shown that the salivary glands of several mosquito species exhibit α-glucosidase activities, the specific enzymes responsible for sugar digestion remain understudied. We therefore expressed and purified three recombinant salivary α-glucosidases from the mosquito vectors Aedes aegypti, Anopheles gambiae, and Culex quinquefasciatus and compared their functions and structures. We found that all three enzymes were expressed in the salivary glands of their respective vectors and were secreted into the saliva. The proteins, as well as mosquito salivary gland extracts, exhibited α-glucosidase activity, and the recombinant enzymes displayed preference for sucrose compared to p-nitrophenyl-α-D-glucopyranoside. Finally, we solved the crystal structure of the Ae. aegypti α-glucosidase bound to two calcium ions at a 2.3 Ångstrom resolution. Molecular docking suggested that the Ae. aegypti α-glucosidase preferred di- or polysaccharides compared to monosaccharides, consistent with enzymatic activity assays. Comparing structural models between the three species revealed a high degree of similarity, suggesting similar functional properties. We conclude that the α-glucosidases studied herein are important enzymes for sugar digestion in three mosquito species.

Primacy of Human Odors Over Visual and Heat Cues in Inducing Landing in Female Aedes aegypti Mosquitoes.

Although human skin odor is thought to be the cue that anthropophilic mosquitoes use to discriminate us from other potential hosts, the precise details of how they use skin odor to find and land on a human is unclear. We found that Aedes aegypti land on a source of skin odor without a co-located visual cue. By collecting human odor on glass beads and using identical glass beads to visually conceal skin odor and heat cues, we were able to study mosquito landing on skin odor, heat, and visual cues separately. Landing is necessary for blood feeding which is a required behavior for the Aedes aegypti life cycle as well as the behavior responsible for the epidemiological impact of mosquitoes. Therefore, we consider it to be the diagnostic measure of the importance of a host cue. In two-choice tests, a skin odor source had the highest valence for landing, followed by a combination of heat and a visual cue, and finally heat and visual cues presented separately. We also measured the durations of the landings, though no significant differences were found. Supplementary Information: The online version contains supplementary material available at 10.1007/s10905-022-09796-2.