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1alc
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(New page: 200px<br /><applet load="1alc" size="450" color="white" frame="true" align="right" spinBox="true" caption="1alc, resolution 1.7Å" /> '''REFINED STRUCTURE OF ...)
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Revision as of 08:49, 20 November 2007
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REFINED STRUCTURE OF BABOON ALPHA-LACTALBUMIN AT 1.7 ANGSTROMS RESOLUTION. COMPARISON WITH C-TYPE LYSOZYME
Overview
The solution of the structure of alpha-lactalbumin from baboon milk (Papio, cynocephalus) at 4.5 A resolution using the isomorphous replacement method, has been reported previously. Initial refinement on the basis of these, low-resolution studies was not successful because of the poor isomorphism, of the best heavy-atom derivative. Because of the striking similarity, between the structure of lysozyme and alpha-lactalbumin, a more cautious, molecular replacement approach was tried to refine the model. Using hen, egg-white lysozyme as the starting model, preliminary refinement was, performed using heavily constrained least-squares minimization in, reciprocal space. The model was further refined using stereochemical, restraints at 1.7 A resolution to a conventional crystallographic residual, of 0.22 for 1141 protein atoms. In the final model, the root-mean-square, deviation from ideality for bond distances is 0.015 A, and for angle, distances it is 0.027 A. The refinement was carried out using the human, alpha-lactalbumin sequence and "omit maps" calculated during the course of, refinement indicated eight possible sequence changes in the baboon, alpha-lactalbumin X-ray sequence. During the refinement, a tightly bound, calcium ion and 150 water molecules, of which four are internal, have been, located. Some of the water molecules were modelled for disordered, side-chains. The co-ordination around the calcium is a slightly distorted, pentagonal bipyramid. The Ca-O distances vary from 2.2 A to 2.6 A, representing a tight calcium-binding loop in the structure. The, calcium-binding fold only superficially resembles the "EF-hand" and, presumably has no evolutionary relationship with other EF-hand structures., The overall structure of alpha-lactalbumin is very similar to that of, lysozyme. All large deviations occur in the loops where all sequence, deletions and insertions are found. The C terminus appears to be rather, flexible in alpha-lactalbumin compared to lysozyme. The experimental, evidence supports the earlier predictions for the alpha-lactalbumin, structure that were based upon the assumption that alpha-lactalbumin and, lysozyme have similar three-dimensional structures, with minimal deletions, and insertions. A detailed comparison of the two structures shows striking, features as well as throwing some light on the evolution of these two, proteins from a common precursor.
About this Structure
1ALC is a Single protein structure of sequence from Papio cynocephalus with CA as ligand. Full crystallographic information is available from OCA.
Reference
Refined structure of baboon alpha-lactalbumin at 1.7 A resolution. Comparison with C-type lysozyme., Acharya KR, Stuart DI, Walker NP, Lewis M, Phillips DC, J Mol Biol. 1989 Jul 5;208(1):99-127. PMID:2769757
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