If nonphosphorylation weakens activity I would assume by default phosphorylation increases activity. The question might be to what extent.
Phosphorylation is tricky as it can increase or decrease activity / interaction. The best I would do is probably either through literature search or perform a docking study on relevant proteins using a phospho protein vs. nonphosphorylated to show phosphorylation does not strengthen protein-protein interaction. Or better, show it experimentally by co-expressing your protein with a GSK, ERK, or likewise that would increase phosphorylation of your protein. Purify it, and carry out a protein-protein binding assay (ITC, fluorescence, whatnot).
It depends on the magnitude of the conformation change and the location of the protein protein binding sites in relation to the phosphorylation sites. Thus it is entirely possible for phosphorylation to increase the interaction of two proteins.
BTW I have a rather avant garde view of the regulation of cell biology via phosphorylation/methylation etc. I published the below paper in the journal Theory in Biosciences on 01/01/2022, I think you may find it of interes.
https://www.researchgate.net/publication/357484839_Is_DNA_repair_controlled_by_a_biological_logic_circuit
I presented on the wider biological implications of this type of regulation in rapid (sub second) decision making, and problem solving in the below linked presentation.
https://www.researchgate.net/publication/373924257_Is_the_cell_a_digitally_controlled_system
All the best, Phil
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