I am learning about protein kinases and I have read that the protein kinase domain is a structurally conserved protein domain containing the catalytic function of protein kinases. I am wondering whether the kinase domain is equivalent to the catalytic domain (the domain that contains the active site) of an enzyme? Any insights are appreciated.
What is a catalytic domain?
Catalysis is the acceleration of a rate of a chemical reaction.
The catalyst is the molecule responsible for catalysis.
A catalytic site is the exact place or region on the catalyst (e.g. enzyme or compound) that is resonsible for catalysis. These are the active sites on enzymes, for example.
A domain is a part of a protein - it may include a site, or it can also refer to the site itself, depending on the context. One can say catalytic domain to mean the exact part of the enzyme that performs the catalysis.
What is a kinase?
Kinases are enzymes that catalyze the transfer of a phosphate group. It's a specific biochemical reaction. In other words, they phosphorylate other molecules with the help of phosphate donor molecules (such as ATP). One part of the kinase is responsible for the catalysis of its phosphorylation reaction, and this part is called the kinase domain. It is, of course, a catalytic domain. More precisely, it is designated a kinase domain.
So, as you can see, now you should understand the following statements:
- All kinase domains are catalytic domains. (Kinase enzymes catalyze phosphorylation!)
- Not all catalytic domains are kinase domains. (Phosphorylation is not the only kind of catalysis!)