Autophosphorylation in signaling — why is it effective? Self-phosphorylation (autophosphorylation) is a powerful way to trigger specific catalytic functions in signaling proteins because it:

Introduction:
Many receptors and kinases activate themselves by adding phosphate groups to specific residues within their own structure. This autophosphorylation event is a classic molecular switch that alters protein conformation and interaction surfaces to drive downstream signaling.

Given Data / Assumptions:

• Tyrosine kinase receptors (e.g., RTKs) and some serine/threonine kinases autophosphorylate upon stimulation.
• Phosphorylation creates docking sites or relieves autoinhibition.
• Conformational changes modulate catalytic efficiency and substrate binding.

Concept / Approach:

Phosphate groups carry negative charge and can reorganize intra-protein hydrogen bonding and electrostatics. This can open an active site, align catalytic residues, or create binding motifs (e.g., SH2/PTB docking), thereby switching on enzymatic activity and assembling signaling complexes.

Step-by-Step Solution:

Verification / Alternative check:

Structural studies reveal activation loop phosphorylation correlating with an open, active conformation and increased catalytic turnover.

Why Other Options Are Wrong:

Option B suggests indiscriminate ligand capture; specificity is maintained by binding pockets, not phosphorylation alone.

Option C confuses membrane permeability with signaling; phosphorylation does not make membranes permeable to hydrophilic ligands.

Option E is incorrect; autophosphorylation activates rather than destroys the kinase domain.

Common Pitfalls:

Assuming phosphorylation only turns proteins on; sometimes it also turns them off, but in the context of activation, conformational change is key.

Final Answer:

Changes the protein’s shape and thereby its enzymatic activity