Human 27‐kDa calbindin complementary DNA sequence

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Abstract
Human 27-kDa calbindin cDNA clones were selected by antibody screening from .lambda.gt11 brain libraries. The sequence revealed an open reading frame coding for a protein of 261 amino acids, containing four active calcium-binding domains, and two modified domains that had presumably lost their calcium-binding capability. Comparison with chick and bovine calbindins showed that the protein was highly conserved in evolution (evolutionary rate: 0.3 .times. 10-9 amio acid-1 year-1) and that active and inactive domains were equally conserved. From the data we postulate that calbindin has an important physiological function involving protein-protein interactions. Comparison of calcium-binding domains from various proteins suggested that all members of the troponin C superfamily derive from a common two-domained ancestor, but that duplications leading to calbindin and to the four-domained calcium-binding proteins took place independently on different branches of the evolutionary tree. Preliminary data showed that another calcium-binding protein, homologous to calbindin, is present in the brain and encoded by a different gene.