Bee stings cause immediate pain, redness, and swelling, largely due to the complex biochemical actions of bee venom components. One of the principal peptides in bee venom is melittin, known for its membrane-binding properties and its ability to activate certain phospholipases in cell membranes. Understanding which phospholipase melittin activates is crucial for grasping the molecular basis of the inflammatory response triggered by bee venom.

This article explains the interaction between melittin and phospholipase enzymes, focusing on the activation of phospholipase A2 (PLA2) and its role in generating arachidonic acid.

Melittin: A Membrane-Binding Peptide in Bee Venom

• Melittin is a small, amphipathic peptide that readily binds to phospholipid membranes.

• Upon binding, melittin disrupts membrane integrity and modulates membrane-associated enzymes.

• It is responsible for much of the pain and local tissue damage caused by bee stings.

Activation of Phospholipase A2 by Melittin

• Melittin activates phospholipase A2 (PLA2), an enzyme that hydrolyzes the sn-2 ester bond of phospholipids.

• PLA2 releases arachidonic acid from membrane phospholipids, a precursor for potent inflammatory mediators such as prostaglandins and leukotrienes.

• Studies have shown that melittin enhances PLA2 activity by altering membrane structure, making phospholipid substrates more accessible to PLA2.

• This activation is synergistic: melittin and PLA2 together cause greater membrane damage and inflammation than either alone.

Why Phospholipase A2 Is the Target

• PLA2 specifically generates arachidonic acid, which is central to the inflammatory cascade.

• Other phospholipases have different roles:

  • Phospholipase C (PLC) generates inositol phosphates and diacylglycerol, involved in signaling but not directly linked to arachidonic acid release.

  • Phospholipase D (PLD) produces phosphatidic acid and inositol derivatives but is not the primary enzyme activated by melittin.

  • Phospholipase A1 (PLA1) removes fatty acids from the sn-1 position but is less involved in inflammation.

Summary of Options

Conclusion

Melittin in bee venom primarily activates phospholipase A2 (PLA2), leading to the release of arachidonic acid from membrane phospholipids. This event triggers a cascade of inflammatory responses responsible for the pain, redness, and swelling following a bee sting.

Correct answer: (2) Phospholipase A2 to generate arachidonic acid