Cloning and expression of a cDNA encoding a new neurocalcin isoform (neurocalcin α) from bovine brain

Neurocalcin (NC), a neuron-specific EF-hand Ca²⁺-binding protein, purified from bovine brain [Terasawa, Nakano, Kobayashi and Hidaka (1992) J. Biol. Chem. 267, 19596–19599] contains multiple isoforms. We previously cloned NCδ from bovine brain and showed high expression in neuronal tissues [Okazaki, Watanabe, Ando, Hagiwara, Terasawa and Hidaka (1992) Biochem. Biophys. Res. Commun. 185, 147–153]. We report here the molecular cloning and expression of a cDNA encoding bovine brain NCα. The translated bovine protein is 191 amino acids long and shares 69.1% of its amino acid sequence with NCδ. Recombinant NCα migrates as a single 23 kDa band and exhibits a Ca²⁺-dependent mobility shift on SDS/PAGE. Analysis of fluorescence emission spectra showed the Ca²⁺-induced peak at 337 nm. Interestingly, the mobility shift and the fluorescence intensity at 337 nm were larger for NCα than for NCδ. In Ca²⁺-overlay experiments, however, the apparent affinity of NCα for ⁴⁵Ca²⁺ was similar to that of NCδ. Immunohistochemical analysis revealed NCα expression in the granular layer of the rat cerebellar cortex whereas NCδ was found in the Purkinje cell layer. In the rat olfactory bulb, NCα was located in external tufted cells, and NCδ was found in the periglomerular cells. These data demonstrate that NC isoforms differ in their tissue distribution and conformational changes induced by Ca²⁺ binding. Thus differential regulation of the two NC isoforms may be involved in control of neuron function.