Membrane-bound sucrose hydrolase contributes to carbohydrate metabolism in Bombyx mori

Insects mainly rely on sucrase to hydrolyze sucrose into glucose and fructose, supplying carbon and energy for growth and development. Although soluble and membrane-associated sucrases have been identified in several insects, the physiological function of the membrane-bound sucrase remains unclear. Here, we performed a comprehensive analysis of the biochemical properties and physiological functions of the membrane-bound sucrase (BmSUH) in Bombyx mori. Immunofluorescence analysis revealed distinct localization patterns of BmSUH and another crucial sucrase, β-fructofuranosidase (BmSUC1) in the midgut. BmSUH was localized to the microvilli of columnar cells, while BmSUC1 was expressed in the cavities of goblet cells. In addition, the N-terminal transmembrane domain is crucial for membrane localization of BmSUH. We then verified that one of the positive selection sites, N326, is N-glycosylated and essential for the enzyme activity of BmSUH. CRISPR/Cas9-mediated knockout of BmSUH significantly reduced both membrane-associated and membrane-bound sucrase activity in the midgut, leading to decreased sucrose absorption from food. Transcriptome analysis further revealed the molecular mechanisms underlying the physiological function of BmSUH, with differentially expressed genes enriched in many pathways related to digestion, absorption, and metabolism of carbohydrates. These results highlight that BmSUH served as an essential sucrase involved in the digestive and metabolic processes. This study provides insight into the functional evolution of the membrane-bound sucrase and advances our understanding of sucrose utilization in lepidopteran insects.