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United States Department of Agriculture

Agricultural Research Service

Title: Protein-Protein Interactions in Casein Micelle Structure

Authors
item Farrell, Harold
item Qi, Phoebe

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: April 12, 2003
Publication Date: May 9, 2003
Citation: Farrell, H.M., Qi, P.X. 2003. Protein-Protein interactions in casein micelle structure. l7th Annual J.R. Brunner Protein Symposium. p.12.

Technical Abstract: Historically, the central dogma of structural biology is the Anfinsen hypothesis: the linear primary sequence of amino acids of a protein codes for specific secondary structural elements which in turn lead to tertiary structural elements through protein folding and complex higher order systems through protein-protein interactions. Recent advances in the field of protein chemistry have significantly enhanced our understanding of the possible intermediates that may occur during productive on-line protein folding. In particular, studies on alpha-lactalbumin have led to the theory that the molten globule state is an intermediate in the folding of many proteins. The molten globule state is characterized by a somewhat compact structure, a higher degree of hydration and side chain flexibility, a significant amount of native secondary structure but little tertiary folds, and the ability to react with chaperones. Purified alpha- sl- and k-caseins share many of these same properties; these caseins may thus occur naturally in a molten globule-like state with defined, persistent structures. These two caseins however appear to proceed to quaternary structures without tertiary folds. The major controversy in the area of casein chemistry is whether or not these protein-protein interactions are true self-association reactions in a biologically productive on-line process or random aggregation reactions; that is, does the Anfinsen hypothesis pertain to caseins. Research in our laboratory has suggested that there are, indeed, persistent secondary structural elements in the caseins and that these elements participate in protein-protein interactions. Under physiological conditions some of these self-associations may play a selective role in the on-line biologically productive process of calcium and phosphate binding and transport (casein micelle formation). Under non-physiological conditions, other aggregation reactions proceed from the molten globule state, and these latter reactions, as they are based upon defined secondary structures, can lead to the reproducible formation of novel polymers with new food functionalities. By taking advantage of these "new views" of protein folding, and applying these concepts to casein interactions, it may be possible to generate new and useful information not only on casein micelle formation but also provide new useful forms of proteins for the food ingredient market.

Last Modified: 9/23/2014
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