Role of phenolic acids with different functional groups in the regulation of starch digestion in simulated dietary intake patterns.

This study investigated the effects of phenolic acids with different functional groups (cinnamic acid: CIA, caffeic acid: CA, ferulic acid: FA) on corn starch (CS) digestibility by simulating dietary intake patterns (co-heating and non-co-heating) and their mechanism. Both treatments could reduce the digestibility of CS. Compared to the non-co-heating treatment, the resistant starch content of 10 % CA co-heating samples increased by 8.36 %. The co-heating case led to a decrease in the trough viscosity, peak viscosity, and final viscosity of CS. Phenolic acids reduced the short-range order of CS, which was due to the interaction through hydrogen bonding by co-heating. The contribution was most pronounced for CA which contained more hydroxyl groups on the benzene ring. Quartz Crystal microbalance tests further confirmed that different absorption of phenolic acids to CS was caused by their hydroxyl groups on the benzene ring. These results demonstrated that the functional groups of phenolic acids were a controllable factor in inhibiting starch digestion, and co-heating could be considered a promising method to control starch digestion and an advocating way to ingest phenolic supplements.

ATP binding by the P-loop NTPase OsYchF1 (an unconventional G protein) contributes to biotic but not abiotic stress responses.

G proteins are involved in almost all aspects of the cellular regulatory pathways through their ability to bind and hydrolyze GTP. The YchF subfamily, interestingly, possesses the unique ability to bind both ATP and GTP, and is possibly an ancestral form of G proteins based on phylogenetic studies and is present in all kingdoms of life. However, the biological significance of such a relaxed ligand specificity has long eluded researchers. Here, we have elucidated the different conformational changes caused by the binding of a YchF homolog in rice (OsYchF1) to ATP versus GTP by X-ray crystallography. Furthermore, by comparing the 3D relationships of the ligand position and the various amino acid residues at the binding sites in the crystal structures of the apo-bound and ligand-bound versions, a mechanism for the protein's ability to bind both ligands is revealed. Mutation of the noncanonical G4 motif of the OsYchF1 to the canonical sequence for GTP specificity precludes the binding/hydrolysis of ATP and prevents OsYchF1 from functioning as a negative regulator of plant-defense responses, while retaining its ability to bind/hydrolyze GTP and its function as a negative regulator of abiotic stress responses, demonstrating the specific role of ATP-binding/hydrolysis in disease resistance. This discovery will have a significant impact on our understanding of the structure-function relationships of the YchF subfamily of G proteins in all kingdoms of life.