Rapid unfolding of pig pancreas α-amylase: Kinetics, activity and structure evolution.

α-Amylase plays an important role in food processing and in-vivo digestion. Many biological functions of α-amylase are affected by unfolding. The pre-steady-state rapid unfolding kinetics of α-amylase remains unknown. In this study, the rapid unfolding kinetics of porcine pancreatic α-amylase (PPA) with guanidine hydrochloride (GdmHCl) were investigated by stopped-flow spectroscopy. Structural characterization of PPA by fluorescence spectroscopy, and molecular dynamics simulation showed that the unfolding process of PPA might start from the internal active center, where the ß-sheet structure was destroyed, followed by the exposure of hydrophobic amino acid residues. Further research revealed that GdmHCl denaturized PPA not by complexing with PPA. The surrounding H-bond network of water was changed by GdmHCl. This research improves our understanding of the unfolding kinetics of the PPA on the microsecond scale. It also provides the evidence experimentally of the surrounding water contribution to protein denaturization.

Quantitative structure-pungency landscape of sanshool dietary components from Zanthoxylum species.

The molecular basis of the pungency of sanshool dietary components from the Zanthoxylum species has been firstly addressed by constructing the statistically significant and highly predictive quantitative structure-pungency relationship models along with the pharmacophore models. The important pungent structural characters in the isobutylamide moiety and linear carbon chains were elucidated in this study that maintained the suitable spatial packing and electrostatic interactions with their receptors. Our results also revealed that the amide moiety, N-isobutyl moiety with suitable bulky and restricted electronegative substituents, and the relatively long straight carbon chains with suitable (conjugated) CC bonds or heteroatoms at regular intervals were essential for the high pungency. The pungency of 42 new sanshools was predicted, compared with the rough experimental data, and ultimately classified into weak, medium and strong types. Most of these sanshools were found to have good oral bioavailability and acceptable pharmacokinetic properties.

Inhibition of starch digestion: The role of hydrophobic domain of both α-amylase and substrates.

The physicochemical mechanism of starch digestion is very complicated since it may be affected by the non-valence interactions of the amylase inhibitor with the substrate or the enzyme. The role of hydrophobic interaction in the process of starch digestion is not clear. In this study, pluronics (PLs) with different hydrophobicity were used as model amphiphilic compounds to study their inhibition on starch digestion using multi-spectroscopic methods. The results showed that the hydrophobic nature of PLs changed starch structure, but it had a greater effect on the structure of α-amylase by exposing more tryptophan residues and increasing α-helix and ß-sheet contents. Further investigation by using different chain-length fatty acids confirmed the results. The finding in this study is informative to design and fabricate α-amylase inhibitors for controlling starch digestion at the molecular level.