This report of the American Dairy Science Association Committee on the Nomenclature, Classification, and Methodology of Milk Proteins reviews changes in the nomenclature of milk proteins necessitated by recent advances of our knowledge of milk proteins. Identification of major caseins and whey proteins continues to be based upon their primary structures. Nomenclature of the immunoglobulins consistent with new international standards has been developed, and all bovine immunoglobulins have been characterized at the molecular level. Other significant findings related to nomenclature and protein methodology are elucidation of several new genetic variants of the major milk proteins, establishment by sequencing techniques and sequence alignment of the bovine caseins and whey proteins as the reference point for the nomenclature of all homologous milk proteins, completion of crystallographic studies for major whey proteins, and advances in the study of lactoferrin, allowing it to be added to the list of fully characterized milk proteins.

The structures of the trigonal crystal form of bovine beta-lactoglobulin variant A at pH 6.2, 7.1, and 8.2 have been determined by X-ray diffraction methods at a resolution of 2.56, 2. 24, and 2.49 A, respectively. The corresponding values for R (Rfree) are 0.192 (0.240), 0.234 (0.279), and 0.232 (0.277). The C and N termini as well as two disulfide bonds are clearly defined in these models. The glutamate side chain of residue 89 is buried at pH 6.2 and becomes exposed at pH 7.1 and 8.2. This conformational change, involving the loop 85-90, provides a structural basis for a variety of pH-dependent chemical, physical, and spectroscopic phenomena, collectively known as the Tanford transition.

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Solutions of bovine β-lactoglobulin (β-Lg) A−C were heated at temperatures between 50 and 90 °C for 12.5 min at pH 6.7 or 7.4, and the products were analyzed by alkaline, sodium dodecyl sulfate (SDS), and two-dimensional (2D) (alkaline and then SDS) polyacrylamide gel electrophoresis (PAGE). Results from the pH 6.7 samples that were ∼70% denatured showed that the proportion of β-Lg that was in very large aggregates was β-Lg C > β-Lg B > β-Lg A. 2D PAGE showed that there were a large number of unexpected intermediate products, especially from β-Lg A. These and other results, including the dissociation of disulfide-bonded dimers from trimers and tetramers by SDS, indicate that (1) β-Lg dimers could be important intermediates in the further aggregation of β-Lg, (2) hydrophobically driven associations occur within the aggregates, (3) the mechanism of β-Lg aggregation is not simple, and (4) differences in variant protein behavior are explainable in terms of net negative charge and specific amino acid substitutions. Keywords: Thermal denaturation; electrophoresis; aggregate formation; hydrophobically associated aggregates; disulfide-linked aggregates; β-lactoglobulin variants; two-dimensional polyacrylamide gel electrophoresis

The X-ray structure of bovine L L-lactoglobulin with the ligand 12-bromododecanoic acid as a model for fatty acids has been determined at a resolution of 2.23 A î in the trigonal lattice Z form. The ligand binds inside the calyx, resolving a long-standing controversy as to where fatty-acid like ligands bind. The carboxylate head group lies at the surface of the molecule, and the lid to the calyx is open at the pH of crystallization (pH 7.3), consistent with the conformation observed in ligand-free bovine L L-lactoglobulin in lattice Z at pH 7.1 and pH 8.2.z 1998 Federation of European Biochemical Societies.

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