Regulation of the plant plasma membrane H+-ATPase by its C-terminal domain: what do we know for sure?
The plant plasma membrane H(+)-ATPase is kept at a low activity level by its C-terminal domain, the inhibitory function of which is thought to be mediated by two regions (region I and II) interacting with cytoplasmic domains essential for the catalytic cycle. The activity of the enzyme is well known to be regulated by 14-3-3 proteins, the association of which requires phosphorylation of the penultimate H(+)-ATPase residue, but can be abolished by phosphorylation of residues close-by. The current knowledge about H(+)-ATPase regulation is briefly summed up here, combined with data that query some of the above statements. Expression of various C-terminal deletion constructs of PMA2, a H(+)-ATPase isoform from Nicotiana plumbaginifolia, in yeast indicates that three regions, which do not correspond to regions I or II, contribute to autoinhibition. Their individual and combined action can be abolished by (mimicking) phosphorylation of three threonine residues located within or close to these regions. With respect to the wild-type PMA2, mimicking phosphorylation of two of these residues increases enzyme activity. However, constitutive activation of wild-type PMA2 requires 14-3-3 association. Altogether, the data suggest that regulation of the plant H(+)-ATPase occurs in progressive steps, mediated by several protein kinases and phosphatases, thus allowing gradual as well as fine-tuned adjustment of its activity. Moreover, mating-based split ubiquitin assays indicate a complex interplay between the C-terminal domain and the rest of the enzyme. Notably, their tight contact does not seem to be the cause of the inactive state of the enzyme.
Speth
Corinna
C
Center for Plant Molecular Biology - Plant Physiology, University of Tübingen, Auf der Morgenstelle 5, 72076 Tübingen, Germany.
Jaspert
Nina
N
Marcon
Caroline
C
Oecking
Claudia
C
D048948:14-3-3 Proteins / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000201:enzymology*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology; D016415:Sequence Alignment; D017384:Sequence Deletion
D048948:14-3-3 Proteins; D010940:Plant Proteins; D006180:Proton-Translocating ATPases; C430720:PMA4 protein, Nicotiana plumbaginifolia