39. In the context of signaling, the enzyme protein kinase C (PKC) depends on multiple molecules for its complete activation. This activation depends on the presence of:
A. phosphatidylserine at the inner leaflet of the plasma membrane.
B. Ca²⁺
C. phosphatidylethanolamine at the inner leaflet of the plasma membrane.
D. diacylglycerol present in the inner leaflet of the plasma membrane.
Which one of the following options represents the combination of all correct molecules?
(1) A, B and C     (2) A, C and D
(3) B, C and D     (4) A, B and D

 

Protein Kinase C (PKC) Activation Requirements: Key Molecules Explained

---

Introduction

Protein kinase C (PKC) is a family of enzymes that play critical roles in cellular signaling pathways, regulating processes like gene expression, cell proliferation, and secretion. The activation of PKC requires the coordinated presence of several molecules that together relieve autoinhibition and promote its kinase activity.

PKC Activation Cofactors

• Phosphatidylserine (PS): This negatively charged phospholipid is localized predominantly to the inner leaflet of the plasma membrane and is essential for anchoring and properly orienting PKC during activation. PS acts as a necessary cofactor enabling PKC to bind membranes and be fully active.

• Calcium Ions (Ca²⁺): Increased intracellular Ca²⁺ concentrations bind to the C2 domain of conventional PKC isoforms (cPKCs), inducing conformational changes that promote membrane association and activation.

• Diacylglycerol (DAG): Generated by receptor-stimulated phospholipase C activity, DAG remains membrane-bound and binds to the C1 domain of PKC, providing a crucial lipid-derived second messenger signal required for PKC activation.

• Phosphatidylethanolamine (PE): Although PE is another abundant phospholipid in the inner leaflet of the plasma membrane, it is not directly involved as a cofactor in PKC activation.

Integration of Signals

The classical (conventional) PKC isoforms require phosphatidylserine, Ca²⁺, and DAG simultaneously for full activation. This synergy ensures that PKC activity is precisely regulated in response to cellular signals like those from G protein-coupled receptors and receptor tyrosine kinases.

Summary of Options

• (1) A, B and C — Includes PE which is incorrect

• (2) A, C and D — Excludes Ca²⁺, essential for activation

• (3) B, C and D — Excludes phosphatidylserine, essential lipid cofactor

• (4) A, B and D — Correct combination: phosphatidylserine (A), Ca²⁺ (B), and DAG (D)

Correct Answer

(4) A, B and D

This combination represents the molecules required for complete PKC activation.

---