What do you mean by crosstalk?

Do you know which residues are modified? You could mutate them individually to see the effect of each PTM.

Thanks for your reply. We found four Ser/Thr/Tyr phosphorylation sites and two Lys acetylation sites on the photosynthetic protein. We have mutated each of them to analyze the effect and found the change of acetylation level in phosphorylation mutations. However, I have no idea how to further corroborate the cross-influence between acetylation and phosphorylation?

Your result suggests 2 possibilities: (1) The enzyme that performs the acetylation reaction recognizes the presence of phosphorylation on the target protein, or (2) phosphorylation causes a conformational change in the target protein that makes it more accessible to the acetylation enzyme. To investigate this, you would ideally have purified acetylation and phosphorylation enzymes and wild-type and mutant target proteins to work with. You could then perform kinetic and binding studies of the acetylation reaction, and do structural studies by x-ray crystallography of phosphorylated and unphosphorylated target protein.

Thanks a lot.

A very nice technique to get in depth Structural information that will be complementary to crystallography is Deuterium Exchange Mass Spectrometry. We've applied it to understand the effects of phosphorylation on JNK activity, see this link:

Article Phosphorylation- and Nucleotide-Binding-Induced Changes to t...