Autoinhibition of a calmodulin-dependent calcium pump involves a structure in the stalk that connects the transmembrane domain to the ATPase catalytic domain.
The regulation of Ca(2+)-pumps is important for controlling [Ca(2+)] in the cytosol and organelles of all eukaryotes. Here, we report a genetic strategy to identify residues that function in autoinhibition of a novel calmodulin-activated Ca(2+)-pump with an N-terminal regulatory domain (isoform ACA2 from Arabidopsis). Mutant pumps with constitutive activity were identified by complementation of a yeast (K616) deficient in two Ca(2+)-pumps. Fifteen mutations were found that disrupted a segment of the N-terminal autoinhibitor located between Lys(23) and Arg(54). Three mutations (E167K, D219N, and E341K) were found associated with the stalk that connects the ATPase catalytic domain (head) and with the transmembrane domain. Enzyme assays indicated that the stalk mutations resulted in calmodulin-independent activity, with V(max), K(mATP), and K(mCa(2+)) similar to that of a pump in which the N-terminal autoinhibitor had been deleted. A highly conservative substitution at Asp(219) (D219E) still produced a deregulated pump, indicating that the autoinhibitory structure in the stalk is highly sensitive to perturbation. In plasma membrane H(+)-ATPases from yeast and plants, similarly positioned mutations resulted in hyperactive pumps. Together, these results suggest that a structural feature of the stalk is of general importance in regulating diverse P-type ATPases.
Curran
A C
AC
Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Hwang
I
I
Corbin
J
J
Martinez
S
S
Rayle
D
D
Sze
H
H
Harper
J F
JF
D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D000595:Amino Acid Sequence; D017360:Arabidopsis; D019703:Calcineurin / Q000235:genetics; D000252:Calcium-Transporting ATPases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D004791:Enzyme Inhibitors; D005656:Fungal Proteins / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D005816:Genetic Complementation Test; D008958:Models, Molecular; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010940:Plant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D053499:Plasma Membrane Calcium-Transporting ATPases; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D006180:Proton-Translocating ATPases / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins
D018528:ATP-Binding Cassette Transporters; D002147:Calmodulin; D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D018832:Molecular Chaperones; C434364:PMA2 protein, S cerevisiae; C085484:PMC1 protein, S cerevisiae; D010940:Plant Proteins; C101767:SSC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D019703:Calcineurin; C092477:PMA1 protein, S cerevisiae; C507517:ATP2B4 protein, human; D006180:Proton-Translocating ATPases; D053499:Plasma Membrane Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases