Pro-Lys

This study assessed the melanogenesis effects of rice protein hydrolysate (RPH) and explored the underlying molecular mechanism of its characteristic peptides. In this investigation, human epidermal melanocyte (PIG1) cells were used to establish a UVB-induced model to evaluate the effect of RPH on melanin content, tyrosinase activity, and reactive oxygen species (ROS) levels. High performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was employed to identify the peptide composition (2-4 amino acids) in RPH. Enzymatic hydrolysis was employed to screen the characteristic peptides Leu-Leu-Lys (LLK), Leu-Pro-Lys (LPK), and pyroGlu-Lys (pEK), while their effect on the molecular mechanism involved in the melanin synthesis process was further explored using quantitative real-time polymerase chain reaction (PCR) and western blotting. The results indicated that RPH reduced the melanin content, tyrosinase activity, and ROS production in PIG1 cells. The selected peptides LLK, LPK, and pEK from RPH reduced the expression of tyrosinase-related protein 1 (TRP-1) and tyrosinase-related protein 2 (TRP-2) and affected melanin synthesis by regulating the JNK/β-Trcp/NFκB-p65/MITF signaling pathway at the mRNA and protein levels. This study shows that RPH plays a vital role in the melanogenesis process, therefore, providing a theoretical basis for the use of RPH as a novel additive product.

Despite a high degree of structural similarity, it is known that MMP2 and MMP9 have distinct roles in the angiogenic switch and in cell migration, as they activate diverse signaling pathways. Indeed, inhibition of MMP2 and MMP9 can show beneficial or detrimental effects depending on the stage of tumor progression. Thus, the selective inhibition of gelatinases is of relevance for a successful drug lead, which has to be achieved despite the high structural similarity of the two gelatinases. Herein, the synthesis and evaluation of d-proline-derived hydroxamic acids containing amino appendages at C-4 as gelatinase inhibitors are reported. Inhibition assays enabled the identification of a > 200-fold selective MMP9 inhibitor when Lys was considered as a C-4 substituent, thus addressing gelatinase selectivity beyond the S1' subsite, which is a major driver for selectivity. Molecular docking studies revealed the basic moiety of Lys as detrimental for inhibition of MMP2 as compared to MMP9.

Short peptides have great potential as safe and effective anticancer drug leads. Herein, the influence of short cyclic peptides containing the Pro-Pro-Phe-Phe sequence on patient-derived melanoma cells was investigated. Cyclic peptides such as cyclo(Leu-Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe-), called CLA, and cyclo(Pro-homoPro-β3homoPhe-Phe-), called P11, exert the cytotoxic and the cytostatic effects in melanoma cells, respectively. CLA was the most active peptide as it reduced the viability of melanoma cells to 50% of control at about 10 µM, whereas P11 at about 40 µM after 48 h incubation. Interestingly, a linear derivative of P11 did not induce any effect in melanoma cells confirming previous studies showing that cyclic peptides exert better biological activity compared to their linear counterparts. According to in silico predictions, cyclic tetrapeptides show a better pharmacokinetic and toxic profile to humans than CLA. Notably, the spatial structure of those peptides containing synthetic amino acids has not been explored yet. In the Cambridge Structural Database, there is only one such cyclic tetrapeptide, cyclo((R)-β2homoPhe-D-Pro-Lys-Phe-), while in the Protein Data Bank-none. Therefore, we report the first crystal structure of cyclo(Pro-Pro-β3homoPhe-Phe-), denoted as 4B8M, a close analog of P11, which is crucial for drug discovery. Comparative molecular and supramolecular analysis of both structures was performed. The DFT findings revealed that 4B8M is well interpreted in the water solution. The results of complex Hirshfeld surface investigations on the cooperativity of interatomic contacts in terms of electrostatic and energetic features are provided. In short, the enrichment ratio revealed O…H/H…O and C…H/H…C as privileged intercontacts in the crystals in relation to basic and large supramolecular H-bonding synthon patterns. Furthermore, the ability of self-assemble 4B8M leading to a nanotubular structure is also discussed.