The self-association and thermal denaturation of caprine and bovine ß-lactoglobulin.

Milk components, such as proteins and lipids, have different physicochemical properties depending upon the mammalian species from which they come. Understanding the different responses of these milks to digestion, processing, and differences in their immunogenicity requires detailed knowledge of these physicochemical properties. Here we report on the oligomeric state of ß-lactoglobulin from caprine milk, the most abundant protein present in the whey fraction. At pH 2.5 caprine ß-lactoglobulin is predominantly monomeric, whereas bovine ß-lactoglobulin exists in a monomer-dimer equilibrium at the same protein concentrations. This behaviour was also observed in molecular dynamics simulations and can be rationalised in terms of the amino acid substitutions present between caprine and bovine ß-lactoglobulin that result in a greater positive charge on each subunit of caprine ß-lactoglobulin at low pH. The denaturation of ß-lactoglobulin when milk is heat-treated contributes to the fouling of heat-exchange surfaces, reducing yields and increasing cleaning costs. The bovine and caprine orthologues of ß-lactoglobulin display different responses to thermal treatment, with caprine ß-lactoglobulin precipitating at higher pH values than bovine ß-lactoglobulin (pH 7.1 compared to pH 5.6) that are closer to the natural pH of these milks (pH 6.7). This property of caprine ß-lactoglobulin likely contributes to the reduced heat stability of caprine milk compared to bovine milk at its natural pH.

Keratin and S100 calcium-binding proteins are major constituents of the bovine teat canal lining.

The bovine teat canal provides the first-line of defence against pathogenic bacteria infecting the mammary gland, yet the protein composition and host-defence functionality of the teat canal lining (TCL) are not well characterised. In this study, TCL collected from six healthy lactating dairy cows was subjected to two-dimensional electrophoresis (2-DE) and mass spectrometry. The abundance and location of selected identified proteins were determined by western blotting and fluorescence immunohistochemistry. The variability of abundance among individual cows was also investigated. Two dominant clusters of proteins were detected in the TCL, comprising members of the keratin and S100 families of proteins. The S100 proteins were localised to the teat canal keratinocytes and were particularly predominant in the cornified outermost layer of the teat canal epithelium. Significant between-animal variation in the abundance of the S100 proteins in the TCL was demonstrated. Four of the six identified S100 proteins have been reported to have antimicrobial activity, suggesting that the TCL has additional functionality beyond being a physical barrier to invading microorganisms. These findings provide new insights into understanding host-defence of the teat canal and resistance of cows to mastitis.

Host defence related responses in bovine milk during an experimentally induced Streptococcus uberis infection.

BACKGROUND: Milk contains a range of proteins of moderate or low abundance that contribute to host defence. Characterisation of these proteins, the extent to which their abundance is regulated by pathogenic stimuli, and the variability of their response between and within individual animals would facilitate a better understanding of the molecular basis for this important function of milk. RESULTS: We have characterised the host defence proteins in bovine milk and their responses to intra-mammary infection by a common Gram positive mastitis pathogen, Streptococcus uberis, using a combination of 2D gel electrophoresis and GeLC mass spectrometry. In total, 68 host defence-associated proteins were identified, 18 of which have a direct antimicrobial function, 23 of which have a pathogen-recognition function, and 27 of which have a role in modulating inflammatory or immune signalling. The responsiveness of seven proteins was quantified by western blotting; validating the proteomic analyses, quantifying the within- and between animal variability of the responses, and demonstrating the complexity and specificity of the responses to this pathogen. CONCLUSIONS: These data provide a foundation for understanding the role of milk in host-microbe interaction. Furthermore they provide candidate biomarkers for mastitis diagnosis, and will inform efforts to develop dairy products with improved health-promoting properties.

Alterations in the salivary proteome associated with periodontitis.

AIM: To identify changes in the salivary proteome associated with active periodontitis. MATERIALS AND METHODS: Quantitative proteomics (two-dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis) was used to investigate whole saliva from individuals with severe periodontitis and their proteomic profiles before and after periodontal treatment were compared. RESULTS: A comparison of 128 proteins across all saliva samples identified 15 protein spots with altered abundance. The predominant alteration observed was an increase in the abundance of the S100 proteins S100A8/A9/A6. Of the remaining proteins with altered abundance, haptoglobin, prolactin inducible protein and parotid secretory protein have previously been associated with host defence. CONCLUSION: These results highlight the predominant involvement of S100 proteins in the host response during periodontitis, identify host defence components that have not been linked previously to this disease and suggest new potential biomarkers for monitoring disease activity in periodontitis.