Inhibition mechanism of human salivary α-amylase by lipid transfer protein from Vigna unguiculata

VuLTP1.1, a LTP1 from Vigna unguiculata, inhibits 78.1 % of the human salivary α-amylase (HSA) activity at 20 μM. We had performed a correlation study between VuLTP1.1 structure and HSA inhibitory activity and showed that two VuLTP1.1 regions are responsible for HSA inhibition. In one of them we had characterized the crucial importance of an Arg₃₉ for inhibition. In this work, we analyzed the VuLTP1.1-HSA interaction by protein-protein docking to understand the most probable interaction model and the mechanism of HSA inhibition by VuLTP1.1. The VuLTP1.1 tertiary structure quality and refinement as well as the docking assay between VuLTP1.1 and HSA were done by bioinformatic programs. HSA inhibition occurs by direct interaction of the VuLTP1.1 with the HSA causing the obstruction of the carbohydrate biding cleft with Gibbs free energy of -18.5 Kcal/mol and the dissociation constant of 2.6E⁻¹⁴ M. The previously identified Arg₃₉ of VuLTP1.1 is burrowed into the active site of the HSA and there it interacts with the Asp₃₀₀ of HSA catalytic site by a hydrogen bond. We had confirmed the importance of the Arg₃₉ of VuLTP1.1 for the HSA inhibition which interacts with the Asp₃₀₀ at the HSA active site. I-2, a LTP-like peptide, presents the same HSA inhibition pattern that VuLTP1.1, which indicates that the inhibition mechanism of the LTPs towards α-amylase is very similar. For the best of our knowledge, it is the first time that the HSA inhibition mechanism was understood and described for the LTP1s using VuLTP1.1 and I-2 as prototype inhibitors.