Crystal structures of the apo- and holomutant human lysozymes with an introduced Ca2+ binding site.
The three-dimensional structures of apo- and holomutant human lysozymes (D86/92 lysozyme), in which a calcium binding site was designed and created for enhancing molecular stability by replacing both Gln86 and Ala92 with aspartic acids, were refined at 1.8-A resolution by x-ray crystallography. The overall structures and crystallographic thermal factors of all three proteins, the apo-, holo-D86/92, and the wild-type human lysozymes, were essentially identical; these results showed that the introduction of the calcium binding site did not affect either the overall structure or molecular rigidity of the proteins. However, structure analyses of the apo-D86/92 lysozyme revealed that the mutations affected the side chain conformation of residue 86 and hydrogen networks between the protein and the internal solvent molecules. In the structure of the holo-D86/92 lysozyme, seven oxygen ligands formed a slightly distorted pentagonal bipyramid around the calcium ion, indicating that the coordination around the calcium ion was quite similar to that in baboon alpha-lactalbumin. The pentagonal bipyramid coordination could be one of the most widely found and appropriate calcium binding schemes in proteins.
Inaka
K
K
Protein Engineering Research Institute, Osaka, Japan.
Kuroki
R
R
Kikuchi
M
M
Matsushima
M
M
D001059:Apoproteins / Q000737:chemistry / Q000648:ultrastructure; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D003461:Crystallography; D006801:Humans; D066298:In Vitro Techniques; D009113:Muramidase / Q000737:chemistry* / Q000648:ultrastructure; D009154:Mutation; D011487:Protein Conformation; D012997:Solvents / Q000737:chemistry; D013329:Structure-Activity Relationship; D014867:Water; D014961:X-Ray Diffraction
D001059:Apoproteins; D002135:Calcium-Binding Proteins; D012997:Solvents; D014867:Water; D009113:Muramidase; D002118:Calcium