Crystal structure of human alpha-lactalbumin at 1.7 A resolution

J Mol Biol. 1991 Sep 20;221(2):571-81. doi: 10.1016/0022-2836(91)80073-4.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Calcium-Binding Proteins / chemistry
  • Humans
  • Lactalbumin / chemistry*
  • Molecular Sequence Data
  • Papio
  • Protein Conformation
  • Stereoisomerism
  • Structure-Activity Relationship
  • Thermodynamics
  • X-Ray Diffraction*


  • Calcium-Binding Proteins
  • Lactalbumin