A-Lactalbumin structure

Because of the high level of identity in amino acid sequence between lysozyme and a-lactalbumin (see Fig. 10), it was inevitable that interest turned to the three-dimensional structure of a-lactalbumin when the structure of lysozyme was determined in 1965 by the group at the Royal Institution. However, there were unforeseen difficulties in the direct experimental determination, as discussed below. Hence, attention was directed to models for the a-lactalbumin structure based on the coordinates for lysozyme and on energy minimization programs. 

Subsequently, the baboon a-lactalbumin structure was refined at 1.7-A resolution by Acharya et al. (1989). Using the structure of domestic hen egg white lysozyme as the starting model, preliminary refinement was made using heavily constrained least-squares minimization in reciprocal space. Further refinement was made using stereochemical restraints at 1.7-A resolution to a conventional crystallographic residual of 0.22 for 1141 protein atoms. 

Of the 150 water molecules in the a-lactalbumin structure, four have been shown to be internal. Of the two cavities in a-lactalbumin, one small cavity around residues Leu-12, Phe-53, Met-90, and Ser-56 is fairly devoid of water. The second channel starts at... 

On the basis of the known structure for c-type lysozyme and the nature of the groups involved in its catalytic activity, and early models of a-lactalbumin structure, there were good structural reasons that militated against a-lactalbumin having lytic activity. This point of view was well developed in the useful reviews by Hill and Brew (1975) and by Brew and Hill (1975). Recent X-ray structural determinations for a-... 

The six major proteins of milk, asl-, o s2-, and /c-casein, jS-lactoglobulin, and a-lactalbumin, contain at least one tryptophan residue [57], the fluorescence of which allows the monitoring of the structural modifications of proteins and their physicochemical environment during the coagulation processes. Emission fluorescence spectra of the protein tryptophanyl residues were recorded for the milk coagulation kinetics induced by... 

Bovine a -lactalbumin (BLA) is a protein whose structure appears to be unusually malleable and, as such, has been the focus of many studies of what is termed the molten globule transition. At low pH, BLA expands and is said to lose tertiary structure, but it maintains substantial secondary structure in a partial unfolding transition (molten globule... 

Bovine a-lactalbumin is one of the two enzymes in lactose synthetase, and its amino acid sequence shows striking similarities to that of lysozyme.118 A model based on the lysozyme model has been built, and the side-chain interactions found are convincing, showing that the model is essentially correct. The active cleft in the crystal is, however, shorter than that in the model, and is consistent with a mono- or di-saccharide as the substrate. Thus, the lysozyme structure may serve as a model for some enzymes that synthesize and hydrolyze carbohydrates. 

Caseins are highly disordered proteins having rather limited secondary structure. This is mainly due to the unusually high proline content, which is fairly uniformly distributed along the polypeptide chain. This feature leads to an open extended structure of the casein molecules which differentiates them from the globular whey proteins like a-lactalbumin and (3-lactoglobulin. The caseins have been described as rheomorphic ... 

Figure 6.18 Transmission electron micrographs of protein structures from solutions of 3 wt% a-lactalbumin incubated with 4 wt% Bacillus licheni-forrnis at 50 °C (75 mM Tris-HCl, pH = 7.5) at different values of the cal-cium/a-lactalbumin molar ratio R. The image dimensions are 2100 nrn x 2600 nm Reproduced from Gravcland-Bikkcr et al. (2004) with permission.

Chrysina, E.D., Brew, K., Acharya, K.R. (2000). Crystal structure ofapo- and liolo-bovine a-lactalbumin at 2.2-A resolution reveals an effect of calcium on inter-lobe interactions. Journal of Biological Chemistry, 275, 37021-37029. 

Kataoka, N., Kuwajima, K., Tokunaga, F., Goto, Y. (1997). Structural characterization of the molten globule of a-lactalbumin by solution X-ray scattering. Protein Science, 6, 422 130. 

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