Tyrosyl-threonine

The C-terminal pentapeptide of peptide T (T5) and a glycosylated analogue (T5GlcNAc) were investigated using 1H NMR spectroscopy to examine the influence of the sugar on the secondary structural characteristics of the peptide. The NMR data confirm the presence of a turn structure amongst an ensemble of predominantly randomly structured species in a solution of 83% TFE/H2O for both peptides. This is in agreement with a previous CD analysis demonstrating the presence of beta-turn. Unlike the CD study, the NMR data do not show a difference in the time-averaged conformation of the glycosylated versus non-glycosylated peptide. These studies suggest that any sugar-peptide interactions which occur in this system are transient in nature, and that they do not greatly influence the local secondary structural characteristics of the peptide. In particular, the turn predisposition already exhibited by the peptide appears to be neither enhanced nor reduced by a neighbouring natural N-glycosylation site. This finding is likely to be of general interest, given the importance of glycosylation as a post-translational modification and that its role in determining protein structure has yet to be characterized.

The octapeptide sequence of peptide T is contained within the envelope of HIV and seems to mediate the viral binding to CD4 expressing cells, including monocytes. The biological activity of the alpha-aminobutyric acid pentapeptide derived from the C-terminal sequence of peptide T, in which the polar side chain of threonine in position 4 is substituted by a hydrophilic group, is measured by the monocyte chemotaxis assay. The chemotactic activity of human monocytes is assessed by determining the concentration at which the pentapeptide analog is maximally active and the effectiveness at that concentration, in comparison with peptide T and two shorter homologs, the pentapeptide and tetrapeptide. These experiments suggest that the synthetic analog is a potent chemotactic factor active at picomolar concentrations and that it competes with peptide T for the monocyte binding site.

The milk and milk products from cows reared under grazing system are believed to be healthier and hence have high demand compared to milk from cows reared in the non-grazing system. However, the effect of grazing on milk metabolites, specifically lipids has not been fully understood. In this study, we used acetonitrile precipitation and methanol:chloroform methods for extracting the milk metabolites followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) run to identify the different metabolites between the milk of grazing and non-grazing early lactating Malnad Gidda cows. Various carbohydrates, amino acids, nucleosides and vitamin derivatives were found to be differentially abundant in grazing cows. A total of 35 metabolites were differentially regulated (fold change above 1.5) between the two groups. Tyrosyl-threonine, histidinyl-cysteine, 1-methyladenine, L-cysteine and selenocysteine showed fold change above 3 in grazing cows. The lipid profile of milk showed a lesser difference between grazing and non-grazing cows as compared to polar metabolites. To the best of our knowledge, this is the largest inventory of milk metabolomics data of an Indian cattle (Bos indicus) breed. We believe that our study would help to emerge a field of Nutri-metabolomics and veterinary omics research.