A calmodulin‐stimulated Ca²⁺‐ATPase from plant vacuolar membranes with a putative regulatory domain at its N‐terminus¹

Abstract

A eDNA, BCAl, encoding a calmodulin-stimulated Ca 2 + -ATPase in the vacuolar membrane of cauliflower (Brassica oleracea) was isolated based on the sequence of tryptic peptides derived from the purified protein. The BCAl eDNA shares sequence identity with animal plasma membrane Ca2+ -A TPases and Arahidopsis thaliana A CAl, that encodes a putative Ca2+ pump in the chloroplast envelope. In contrast to the plasma membrane Ca2+ -ATPases of animal cells, which have a calmodulin-binding domain situated in the carboxy-terminal end of the molecule, the calmodulin-binding domain of BCAt is situated at the amino terminus of the enzyme.

Identification of a Calmodulin-Regulated Soybean Ca2+-ATPase (SCA1) That Is Located in the Plasma Membrane

“…Conserved amino acid residues of CaMBD1 and other CaMBDs were aligned with these important positions. The other CaMBDs were ACA2p (Harper et al, 1998), BCA1p (Malmstrom et al, 1997), plasma membrane Ca 2ϩ pump (PMCA; Kataoka et al, 1991), calcineurin (Kincaid et al, 1988), and calmodulin (CaM) kinase II (Meader et al, 1993). (B) Amino acid residues 21 to 38 of SCA1p, plotted as an ␣-helical wheel.…”

“…Without optically sectioning the cells, we could see that the fluorescent signal appeared to cover the entire surface of the cell (data not shown). Optical sectioning through the center SCA1p, ACA2p (Harper et al, 1998), and BCA1p (Malmstrom et al, 1997) are identical to gene products of SCA1 (GenBank accession number AF195028), ACA2 (GenBank accession number AF025842), and BCA1 (EMBL accession number X99972), respectively. Identical residues are indicated with dots.…”

“…Type IIB Ca 2 ϩ pumps include the plasma membrane-type Ca 2 ϩ -ATPases, first characterized in animals (Carafoli, 1994), and a subgroup of novel Ca 2 ϩ pumps recently identified in plants, including ACA2p (Harper et al, 1998), which was identified from the model plant system Arabidopsis, and BCA1p (Malmstrom et al, 1997), identified from cauliflower. In contrast to type IIA Ca 2 ϩ pumps, type IIB Ca 2 ϩ pumps are stimulated by binding calmodulin.…”

“…The Plant Cell plants, including ACA2p (Harper et al, 1998), which was identified from the model plant system Arabidopsis, and BCA1p (Malmstrom et al, 1997), identified from cauliflower. In contrast to type IIA Ca 2 ϩ pumps, type IIB Ca 2 ϩ pumps are stimulated by binding calmodulin.…”

“…First, the plant isoforms have regulatory domains located at the N terminus instead of the C terminus of the pump and show little sequence identity to the regulatory domain of an animal pump. Second, unlike type IIB pumps from animals, which are thought to be located exclusively in the plasma membrane, the plant isoforms have been found only in non-plasma membrane locations, such as ACA2p in the ER membrane (Hong et al, 1999), BCA1p in the tonoplast (Malmstrom et al, 1997), and ACA1p, which is thought to reside in the chloroplast inner membrane (Huang et al, 1993). Despite the biochemical evidence for a calmodulin-regulated Ca 2 ϩ -ATPase in the plant cell plasma membrane (Evans, 1994;Askerlund, 1997;Dainese et al, 1997;Hwang et al, 1997;Bonza et al, 1998), the corresponding gene for this has not been cloned, and it is not known whether the anticipated pump is more similar to an animal type IIB pump or to the calmodulin-regulated pumps found in plant cell endomembranes.…”