Question

Autophosphorylation is done on

• A. His residues
• B. Ser/Thr residues
• C. Cys residues
• D. Lys residues

Hint:

Histidine kinase autophosphorylation is crucial in bacterial signaling and differs from the typical phosphorylation of Ser/Thr in eukaryotic kinases.

Answer 1

The Correct Option is A

Step 1: Understanding autophosphorylation.
Autophosphorylation refers to a process where a kinase enzyme catalyzes the transfer of a phosphate group to itself, typically on specific amino acid residues. In protein kinases, this often occurs on histidine (His) residues in certain types of kinases, such as those in bacterial systems.
Step 2: Analyzing the options.
(1) His residues: Correct — Histidine residues are commonly phosphorylated in autophosphorylation, particularly in histidine kinase proteins.
(2) Ser/Thr residues: This is incorrect. Serine and threonine residues are commonly phosphorylated in eukaryotic protein kinases, but not in autophosphorylation.
(3) Cys residues: This is incorrect. Cysteine residues do not typically participate in autophosphorylation.
(4) Lys residues: This is incorrect. Lysine residues are not typically involved in autophosphorylation.
Step 3: Conclusion.
The correct answer is (1) His residues, as autophosphorylation typically occurs on histidine residues in histidine kinases.

Answer 2

Autophosphorylation means a kinase transfers a phosphate group onto itself, and which residue accepts that phosphate depends on the type of kinase system involved. Reviewing each candidate residue:

1. His residues: In histidine kinase systems, which form the sensor component of two-component signal transduction systems, the kinase autophosphorylates on a histidine residue within its own dimeric structure, using the imidazole nitrogen as the phosphate acceptor, before passing that phosphate on to a response regulator.
2. Ser/Thr residues: Serine and threonine are the classic phosphorylation sites used by many eukaryotic protein kinases when phosphorylating their downstream substrates, but this general substrate-phosphorylation chemistry is a separate case from the specific autophosphorylation event asked about here.
3. Cys residues: Cysteine's thiol group participates in other kinds of covalent modification (such as disulfide bond formation or palmitoylation) but is not the phosphate-accepting residue used in kinase autophosphorylation.
4. Lys residues: Lysine's amine side chain is used in modifications like ubiquitination, acetylation, or methylation, not in accepting a phosphate group during autophosphorylation.

The specific self-phosphorylation event referred to here uses the histidine residue as the phosphate acceptor, distinguishing it from general substrate phosphorylation on serine/threonine.

Therefore, the correct answer is His residues.