In silico modeling and in vitro evaluation of antidiabetic potential of exopolysaccharides from Brassicaceae root endophytic bacteria

Abstract

Endophytic bacteria associated with Brassicaceae roots produce extracellular polysaccharides (EPS) that may inhibit carbohydrate-hydrolyzing enzymes related to antidiabetic properties. This study evaluated EPS produced by Brassicaceae root endophytes for inhibitory activity against carbohydrate-digesting enzymes and examined putative ligand–enzyme interactions using molecular docking. Endophytic bacteria were isolated from roots of cabbage, broccoli, Chinese broccoli, and pakcoy, phenotypically characterized, and identified by 16S rRNA gene sequencing. Crude EPS were extracted from bacterial cultures and quantified as dry weight, with total carbohydrate (glucose equivalents) and protein contents determined for compositional comparison. α-Glucosidase inhibitory activity was assessed in vitro using p-nitrophenyl-α-D-glucopyranoside as the substrate, and IC50 values were calculated from dose–response curves with acarbose as a positive control. In silico docking was performed against α-glucosidase (PDB: 2QMJ) using EPS-related monosaccharides, and pose reliability was evaluated by RMSD. Ten isolates produced EPS with yields ranging from 76.7 to 309.7 mg L−1. EPS-associated glucose equivalents ranged from 22.7 to 68.8 mg L−1 and protein from 22.8 to 46.7 mg L−1, indicating isolate/strain-dependent compositional variation. Two crude EPS samples showed the strongest α-glucosidase inhibition, with IC50 values of 121.16 ppm (Pseudomonas plecoglossicida AK8A4) and 168.72 ppm (Neobacillus drentensis AK4B2), whereas the remaining samples showed IC50 values >200 ppm; acarbose yielded an IC50 of 79.79 ppm. Docking produced stable poses (RMSD <2 Å) and predicted stronger binding for acarbose than for individual monosaccharides; among the latter, D-mannose showed the most favorable energy against α-glucosidase. Brassicaceae root bacterial endophytes produced crude EPS with potential α-glucosidase inhibitory activity, supporting further purification and structure–activity analysis to define active fractions and inhibitory mechanisms.