Parvalbumin in Non-Muscle Cells

Abstract

Cells have developed an elaborate system of proteins which specifically interact with calcium ions regulating transmission and reception of the calcium signal. The major task of these proteins which bind calcium with high affinity is to mediate the calcium signal intracellularly and to fine-tune the calcium levels. In some of these proteins an α-helix-loop-α-helix arrangement of the peptide chain has been found and the calcium binding residues are located in the loop connecting the two α-helices. This arrangement is referred to as the “EF-hand” structure, and is derived from the first three-dimensional structure analysis done on carp parvalbumin 4.25 by Kretsinger and Nockolds (1973). This carp parvalbumin structure is the basis of our understanding of how proteins bind calcium with high affinity. The essence of Kretsinger’s hypothesis is that when calcium is acting as a second messenger, its targets are proteins which contain EF-hand structures. In proteins which belong to this family the residues involved in calcium binding are especially well conserved. This has been recently confirmed by X-ray analysis of calmodulin (Babu et al. 1985), troponin C (Herzberg and James 1985; Sundaralingam et al. 1985) and intestinal calcium-binding protein (calbindin-D-10K; Szebenyi et al. 1981; Szebenyi and Moffat 1986).