Chiral implications on Fmoc-dipeptide self-assembly and catalytic kinetics of thermolysin

It is well known that the diverse biocatalysis in living systems are chirality-dependent, but so far, the principle has not been fully revealed. Hence, series of fluorenylmethoxycarbonyl-dipeptide (Fmoc-dipeptide) substrates are designed and varied in sequence and amino acid chirality to further explore the chiral catalytic kinetics of thermolysin. The results demonstrate that the chirality features of the constituent amino acids of Fmoc-dipeptides have significant effect on their supramolecular morphology and chirality. In the thermolysin-catalyzed reaction, the enzyme shows stereoselectivity and preferably screens out the dipeptide substrates consisting solely of l-amino acids to perform catalytic action. The presence of d-amino acids at either end of the target peptide bond will significantly resistant to the catalysis by thermolysin, leading to the catalytic efficiency reduced from 63.8 %-100 % to less than 9.6 %. This is well explained by the molecular docking results that the binding distance for the d-amino acid-containing group is found to be 1.8, 1.4 and 1.7-folds than the corresponding group composed entirely of l-amino acids, respectively. This study is helpful to better understand the specific chiral selection mechanism for enzyme catalysis in biological process, and may have some guidelines for biocatalysis. Furthermore, our findings may provide meaningful insights into understanding the occurrence of the diseases associated with the accumulation of d-amino acids in human body.