Isolation and Characterization of a Calmodulin-binding Ca^2+-ATPase 2 (SCA2) in Soybean

Abstract

We previously reported the isolation and characterization of a gene, SCA1 (for soybean Ca^2+-ATPase 1), encoding a calmodulin-regulated Ca^2+-ATPase that is located in the plasma membrane in soybean. Here, a Ca^2+-ATPase designated as SCA2 was isolated from soybean. The two Ca^2+-ATPases, SCA1 and SCA2, share a remarkably high degree of similarity (78%). Ten transmemebrane domains were predicted by hydropathy analysis. Using gel overlay assays, CaM was found to bind to SCA2 in a Ca^2+-dependent manner. Southern blot analysis revealed the presence of two copies of the Ca^2+-ATPase gene in the soybean genome. An N-terminal truncation mutant that deletes sequence through the putative calmodulin binding site was able to complement a yeast mutant (K616) that was deficient in two endogenous Ca^2+ pumps. Our results indicate that SCA2 is structurally highly conserved with type IIB Ca^2+ pumps in plants.