chapter  5
12 Pages

The EF-Hand Calcium-Binding Proteins

The members of the EF-hand CBPs share a general structural feature of possessing variable numbers of domains that bind to Ca

with high specificity and affinity. The EF-hand structural motif was first reported from the crystal structure of carp parvalbumin (Kretsinger and Kockolds, 1973; Kretsinger, 1980). Specific structural features have been defined as being necessary for calcium binding. The EFhand consists of a consensus sequence of 12 amino acid residues in a helix-loophelix configuration that can ligate Ca

(Linse and Forsen, 1995). The Kretsinger principle states that calcium binding is coordinated by five oxygen-containing amino acid residues and a conserved glycine residue, which causes the bending of the loop. The calcium-binding affinities of these proteins range from K

d

to 10

M

, and this is dependent on the amino acid sequence of the EF-hand loop. EF-hand loops occur as a pair with antiparallel

β

-sheet interaction between the two loops. A high degree of cooperativity exists between calcium-binding loops (M. Zhang

et al.