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Background: Bacterial infections are a major challenge in food processing and public health, and there is an urgent need to develop novel antimicrobial agents. Objectives: The purpose of this study is to investigate the potential mechanism and key components of Pinctada martensii antimicrobial proteins (Pm-Aps) to provide a theoretical basis for the development of novel antimicrobial agents. Methods: The researchers used Vibrio parahaemolyticus (VP) to stimulate Pinctada martensii, extracted the antimicrobial proteins, and analyzed their antimicrobial activities, potential mechanisms of action, and key components using proteomics. Results: The results showed that the antimicrobial activity of Pm-Aps, with broad-spectrum antimicrobial effects, was significantly enhanced after VP stimulation. This was associated with the upregulation of LAAO, CHDH, TLR2, ATG16L1, BAK, CLCA4, and CASP8 and the downregulation of MCM3, MCM5, DTYMK, PLK1, FBXO6, LPCAT3, GST, LAMTOR5, CYP17A, CTSA, and RRM1. It is hypothesized that these proteins may inhibit bacterial growth and multiplication by activating immune-related signaling pathways, inhibiting DNA replication and repair, and inducing apoptosis and autophagy. Furthermore, it was found that LAAO may be a key component of the antimicrobial action of Pm-Aps, killing bacteria by catalyzing the oxidation of amino acids to produce hydrogen peroxide (H2O2). Conclusions: These results strongly suggest that Pm-Aps is an effective antimicrobial protein, and it is expected that new LAAO can be obtained from Pm-Aps. [ABSTRACT FROM AUTHOR]

Pearl and nacre powders have been valuable traditional Chinese medicines with whitening properties for thousands of years. We utilized a high-temperature and high-pressure method along with compound enzyme digestion to prepare the enzymatic hydrolysates of nacre powder of Pinctada martensii (NP-PMH). The peptides were identified using LC–MS/MS and screened through molecular docking and molecular dynamics simulations. The interactions between peptides and tyrosinase were elucidated through enzyme kinetics, circular dichroism spectropolarimetry, and isothermal titration calorimetry. Additionally, their inhibitory effects on B16F10 cells were explored. The results showed that a tyrosinase-inhibitory peptide (Ala-His-Tyr-Tyr-Asp, AHYYD) was identified, which inhibited tyrosinase with an IC50 value of 2.012 ± 0.088 mM. The results of the in vitro interactions showed that AHYYD exhibited a mixed-type inhibition of tyrosinase and also led to a more compact enzyme structure. The binding reactions of AHYYD with tyrosinase were spontaneous, leading to the formation of a new set of binding sites on the tyrosinase. The B16F10 cell-whitening assay revealed that AHYYD could reduce the melanin content of the cells by directly inhibiting the activity of intracellular tyrosinase. Additionally, it indirectly affects melanin production by acting as an antioxidant. These results suggest that AHYYD could be widely used as a tyrosinase inhibitor in whitening foods and pharmaceuticals. [ABSTRACT FROM AUTHOR]

Pinctada martensii muscle proteins were separated into water-soluble, salt-soluble and insoluble protein fractions. The salt-soluble protein fraction was the most abundant, comprising approximately 66.3% of the protein, followed by the water-soluble and insoluble protein fractions in decreasing order. sodium dodecyl sulphate polyacrylamide gel electrophoresis profiles showed that 35- and 97-kDa peptides represented the highest proportions of the water-soluble and salt-soluble protein fractions, respectively. The three protein fractions contained high levels of flavourful amino acids (Glu, Asp, Ala and Lys), with the water-soluble protein fraction having the highest level (47.1%). The size exclusion chromatography profiles of the water-soluble and salt-soluble protein pancreatin hydrolysate demonstrated no significant differences in the molecular weight distributions in the >20 000, 5000-10 000 and 2000-5000 Da fractions, while those of the insoluble protein pancreatin hydrolysate were different. In conclusion, the results provided some basic information that would contribute to the utilisation of these protein fractions. [ABSTRACT FROM AUTHOR]