Quantitative stoichiometry of phosphorylation of the regulatory C-terminus in mutant Arabidopsis plasma membrane proton pumps

摘要

In the aha1-6 mutant significantly decreased levels of AHA1 were detected as expected from a loss-of-function (knock down) mutation. Similar results were seen for the AHA2 unmodified peptide in the aha2-4 mutant sample, suggesting only a small amount of protein is being produced, or is functional, in the insertional mutants. Upregulation of AHA1 in the aha2-4 mutants (and visa versa) was not detected, suggesting there is no compensation occurring at the translation level in the mutant plants. However, the significant changes in the levels of phosphorylation in the mutants is consistent with an increase in kinase mediated phosphorylation behaving as a posttranslational means of compensating for the loss of one protein, by increased phosphorylation of the other. This data indicate there is posttranslational machinery in operation for penultimate threonine phosphorylation, which attempts to compensate for the loss by increasing the catalytic activity of the remaining proteins.