Crystal structure of human alpha-lactalbumin at 1.7 A resolution.
The three-dimensional X-ray structure of human alpha-lactalbumin, an important component of milk, has been determined at 1.7 A (0.17 nm) resolution by the method of molecular replacement, using the refined structure of baboon alpha-lactalbumin as the model structure. The two proteins are known to have more than 90% amino acid sequence identity and crystallize in the same orthorhombic space group, P2(1)2(1)2. The crystallographic refinement of the structure using the simulated annealing method, resulted in a crystallographic R-factor of 0.209 for the 11,373 observed reflections (F greater than or equal to 2 sigma (F)) between 8 and 1.7 A resolution. The model comprises 983 protein atoms, 90 solvent atoms and a bound calcium ion. In the final model, the root-mean-square deviations from ideality are 0.013 A for covalent bond distances and 2.9 degrees for bond angles. Superposition of the human and baboon alpha-lactalbumin structures yields a root-mean-square difference of 0.67 A for the 123 structurally equivalent C alpha atoms. The C terminus is flexible in the human alpha-lactalbumin molecule. The striking structural resemblance between alpha-lactalbumins and C-type lysozymes emphasizes the homologous evolutionary relationship between these two classes of proteins.
Laboratory of Molecular Biophysics, Oxford, England.
K R
KR
Acharya
J S
JS
Ren
D I
DI
Stuart
D C
DC
Phillips
R E
RE
Fenna
D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry; D006801:Humans; D007768:Lactalbumin / Q000737:chemistry*; D008969:Molecular Sequence Data; D010215:Papio; D011487:Protein Conformation; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014961:X-Ray Diffraction
D002135:Calcium-Binding Proteins; D007768:Lactalbumin