# Functional Analysis of Amino Acid Residues Responsible for Substrate Specificity of GH13_17 α‑Glucosidase from Aedes aegypti Saliva (AaMalI)

## TL;DR

This study identifies key amino acid residues in an enzyme from mosquito saliva that determine its sugar preference, offering insights for mosquito control.

## Contribution

The study reveals specific mutations that alter substrate preference in AaMalI, providing structural insights for vector control.

## Key findings

- AaMalI shows optimal activity at pH 6.3 and 40°C with a preference for sucrose over maltose.
- Mutations Y223H and P222N/Y223H switch substrate preference from sucrose to maltose.
- Structural analysis shows Tyr292 and His223 influence substrate binding and hydrolysis.

## Abstract

The α-glucosidase (AaMalI) in Aedes
aegypti saliva belongs to glycoside hydrolase family
13, subfamily 17 (GH13_17)
and plays a crucial role in the digestion of sucrose, which is the
main sugar involved in insect metabolism. The amino-acid residues
in the conserved region II have been reported as the key residues
for sucrose specificity in GH13_17. Using mutagenesis, this study
expressed and purified recombinant AaMalI and determined the molecular
mechanism related to substrate specificity. The optimal activity was
at pH 6.3 and 40 °C. AaMalI had a trisaccharide specificity similar
to GH13 α-glucosidases and preference for sucrose over maltose.
The single mutation of Y223H and the double mutation of P222N/Y223H
altered the substrate preference from sucrose to maltose. Structural
analysis of the AaMalI model obtained by superimposition with the
maltose-bound complex suggested that Tyr292 stabilizes the d-glucosyl moiety at subsite +1, whereas His223 indirectly contributes
to maltose hydrolysis. These findings provide structural insights
into AaMalI substrate specificity and support its potential as a target
for vector mosquito control.