Homology modelling and structural analysis of Solanum tuberosum vacuolar acid invertase

are highly regulated enzymes with essential functions in carbohydrate transport and partitioning, sugar signalling, seed development and plant development. Plant possess three types of invertases, which are located in the apoplast, the cytoplasm and the vacuole, respectively. Homology model of Solanum tuberosum vacuolar acid invertase (St-vaINV) was constructed using Arabidopsis cell-wall invertase (At-cwINV1) and Cichorium intybus (1-FEH IIa ) as a template which showed its overall structure was similar to the glycoside hydrolase family 32 (GH32) enzymes. The three highly conserved motifs, NDPNG, RDP and EC, were located within the active site and involved in catalyzing sucrose hydrolysis. The residues N22, D23, R148, E203, D149 and D239, together with the conserved W20, W47 and W82 residues forming a hydrophobic zone, were necessary to create the ideal sucrose-binding pocket. The docking studies suggested that the sucrose binding catalytic domain of St-vaINV had several minor but potentially important structural differences to that At- cwINV1 resulting in altered affinity for sucrose binding.