A group of calcium-binding proteins which bind to biomembranes has recently been identified in widely different cells and tissues (refs 1-7, reviewed in ref. 8). Three of these proteins (p70, p36 and p32.5) cross-react with antiserum to calelectrin, a Ca2+-binding protein (relative molecular mass 34,000 (34K] from the ray Torpedo marmorata, giving rise to their designation as calelectrin-related proteins. We now report that calelectrin, p36 and p32.5 contain a 17-amino-acid consensus sequence which is conserved and present in multiple copies. We suggest that this sequence may be common to other members of this new group of Ca2+-binding proteins and may underlie their unusual mode of combination with biomembranes.

In a new approach to isolating proteins which participate in the Ca2+-dependent regulation of membrane traffic in animal cells, two new Ca2+-binding proteins (Mr 67 000 and 32 500) have been identified in and purified from bovine liver, brain, and adrenal medulla. These proteins specifically and reversibly bind to chromaffin granule membranes at low Ca2+ concentrations (half-maximal binding at 5.5 microM Ca2+) and greatly potentiate the Ca2+-induced aggregation of these membranes at higher concentrations (above 10 microM). In the presence of ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetate, the isolated proteins have Stokes radii of 3.40 nm (Mr 67 000) and 2.53 nm (Mr 32 500) as estimated by gel filtration and therefore occur as monomers. They are slightly acidic proteins with pI's of 5.85 and 5.60. In bovine tissues, both proteins and a third protein of Mr 35 000 cross-react immunologically with each other and with Torpedo calelectrin (Mr 34 000) and are therefore identified as mammalian calelectrins. In all tissues of Torpedo marmorata tested, only a single molecular mass form of calelectrin exists, whereas multiple forms of calelectrin exist in mammalian tissues, indicating gene duplication during evolution. We suggest that the evolutionary conservation and diversification, the high tissue concentrations, and the Ca2+-specific interactions of the calelectrins make them candidates for Ca2+-dependent regulators of membrane events in animal cells.

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