Met-Glu

Increasing evidence has shown that collagen peptides had various biological activities. In this study, a novel antiplatelet peptide Met-Glu (ME) was separated and identified from silver carp skin by YMC ODS-A C18 separation and ESI-MS/MS analysis. Peptide ME inhibited platelet aggregation and secretion of platelet granules induced by ADP, thrombin and collagen, and significantly attenuated ferric chloride-induced thrombus formation in rats. It did not prolong the bleeding time in mice even at the dose of 300 μmol/kg body weight that showed potent anti-thrombosis effects. Additionally, peptide ME targeted at Gq-protein to downregulate the phosphorylation of PLCβ, an important upstream effector of PI3K/Akt and Erk/MAPK signaling to inhibit intracellular calcium ion mobilization. These results suggest that peptide ME inhibited thrombosis in vivo and inhibited Gq-mediated signaling in platelets, indicating the possibility that ME could potentially be developed as a novel therapeutic agent in the prevention and treatment of thrombotic diseases. PRACTICAL APPLICATIONS: Cardiovascular diseases (CVDs) are the leading cause of mortality and morbidity worldwide. The proximal cause of CVDs is intravascular thrombosis formation, which mostly results from platelet activation, aggregation, and granules secretion. Traditional drugs in the prevention of thrombotic disease, such as aspirin and clopidogrel, are still limited for their side effects, especially bleeding complications. Collagen is a natural source for bioactive peptides and our previous study has shown that collagen peptides could inhibit platelet aggregation in vitro. Understanding the mechanism of collagen peptides on regulation of platelet activation and their in vivo anti-thrombosis activities were important for the development of novel-specific medical food in the prevention of thrombotic diseases.

Chemotaxis of rabbit peritoneal leucocytes stimulated by fMet-Leu-Phe, a synthetic chemoattractant, was inhibited by Glu-Glu-Glu-Glu-Tyr-Pro-Met-Glu (MT peptide) and Leu-Ile-Glu-Asp-Asn-Glu-Tyr-Thr-Ala-Arg-Glu-Gly (Src peptide). Both peptides did not inhibit the binding of [3H] formyl-NLe-Leu-Phe, a chemoattractant, to neutrophils, suggesting that the peptides inhibit the events distal to the chemotactic receptors. These peptides blocked the release of arachidonic acid from phospholipids in neutrophils stimulated with chemoattractants, whereas they had no effect on phospholipase A2 activity itself. The peptides markedly reduced the phosphorylation of lipomodulin, a phospholipase inhibitory protein, in either intact cells or isolated plasma membranes. Lipomodulin immunoprecipitated by monoclonal anti-lipomodulin antibody had phosphorylserine and phosphoryltyrosine as analyzed upon electrophoresis. The MT peptide which does not contain threonine or serine was phosphorylated by isolated plasma membranes. These results, taken together, suggest that a tyrosine phosphorylating kinase is involved in biochemical events of chemotactic receptors, and that lipomodulin is a substrate for this kinase.

A combined chemical ionisation and tandem mass spectrometry (MS/MS) approach has been used for investigation of the gas-phase ion chemistry of systems containing the amino acids Glu and Met, and the dipeptides gamma-Glu-Met and Met-Glu. The metastable fragmentation of the protonated dimer, (Glu)2H(+), reveals an intracluster reaction leading to the elimination of the Glu residue. The main features of the ion-molecule reactions observed in the systems containing Glu and Glu + Met can be described in terms of sequential adduct formation. The results obtained for the thermal dehydration of Glu were used to rationalise the formation of the proton-bound structures (Glu-H2O...H(+)...(Glu-H2O) and (Glu-H2O)3-H(+). The adduct ions, [(Glu-H2O) + H + Glu](+) and [(Glu-H2O) + H + Met](+), and further association products were also observed. The results lead to a reconsideration of the structural aspects proposed earlier for these species in the sense that they suggest that the systems correspond to a mixture of isomeric covalent and proton-bound structures. The thermal effects on the decomposition of the neutral (gamma-Glu-Met) and its protonated form, (gamma-Glu-Met)H(+), at m/z 279 were investigated, and dramatic changes in the MI spectra of the m/z 279 ion with temperature were found. A mechanistic explanation for the observed evolution of higher mass ion peaks in the mass spectra is developed.