I have come to understand that phosphorylation plays a significant role in the (de)activation of certain proteins. I'm now trying to understand this mechanisms in more detail. Specifically, how the addition of a phosphate group can regulate protein activity. Can anyone point me to a source where I can find such an explanation?
The mechanism depends on the exact protein being studied, so if you want a more detailed understanding of the mechanism, you'll have to pick a particular enzyme you'd like to study (good, well studied examples include Src kinase and CDK1). In general, however, there are two main ways that phosphorylation could modulate a protein's function:
1) Directly by changing the structure of the protein. Adding a large, negatively-charged phosphate group to a particular residue can make or break important intramolecular interactions within a protein changing its shape (and therefore its function). A good example here is the protein tyrosine kinase Src.
2) Indirectly by influencing its interaction with other proteins. Phosphorylation can create or occlude protein-protein interaction sites, which can modulate the interaction of proteins with their substrates or other factors that modulate their activity. Good examples here are the phosphorylation of the C-terminal tail of RNA Polymerase II, which acts as a scaffold to recruit different sets of proteins during the different stages of transcription, or how phosphorylation of various cell cycle proteins enables their interaction with ubiquitin ligase enzymes, targeting them for degradation (the [ulr=[PLAIN]https://www.ncbi.nlm.nih.gov/books/NBK26824/]cell[/PLAIN] cycle[/url] provides a nice example of a process with various proteins under control by phosphorylation).