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A novel calmodulin-regulated Ca2+-ATPase (ACA2) from Arabidopsis with an N-terminal autoinhibitory domainTo study transporters involved in regulating intracellular Ca2+, we isolated a full-length cDNA encoding a Ca2+-ATPase from a model plant, Arabidopsis, and named it ACA2 (Arabidopsis Ca2+-ATPase, isoform 2). ACA2p is most similar to a "plasma membrane-type" Ca2+-ATPase, but is smaller (110 kDa), contains a unique N-terminal domain, and is missing a long C-terminal calmodulin-binding regulatory domain. In addition, ACA2p is localized to an endomembrane system and not the plasma membrane, as shown by aqueous-two phase fractionation of microsomal membranes. ACA2p was expressed in yeast as both a full-length protein (ACA2-1p) and an N-terminal truncation mutant (ACA2-2p; Delta residues 2-80). Only the truncation mutant restored the growth on Ca2+-depleted medium of a yeast mutant defective in both endogenous Ca2+ pumps, PMR1 and PMC1. Although basal Ca2+-ATPase activity of the full-length protein was low, it was stimulated 5-fold by calmodulin (50% activation around 30 nM). In contrast, the truncated pump was fully active and insensitive to calmodulin. A calmodulin-binding sequence was identified within the first 36 residues of the N-terminal domain, as shown by calmodulin gel overlays on fusion proteins. Thus, ACA2 encodes a novel calmodulin-regulated Ca2+-ATPase distinguished by a unique N-terminal regulatory domain and a non-plasma membrane localization.
Document ID
Document Type
Reprint (Version printed in journal)
External Source(s)
Harper, J. F.
(The Scripps Research Institute La Jolla, California 92037, United States)
Hong, B.
Hwang, I.
Guo, H. Q.
Stoddard, R.
Huang, J. F.
Palmgren, M. G.
Sze, H.
Evans, M. L.
Date Acquired
August 22, 2013
Publication Date
January 9, 1998
Publication Information
Publication: The Journal of biological chemistry
Volume: 273
Issue: 2
ISSN: 0021-9258
Subject Category
Life Sciences (General)
Distribution Limits
Non-NASA Center
NASA Discipline Plant Biology

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