Styloidiin

Styloidiin is a protein found in the venom of the styloid honey bee, Melissodes styloides. It is a member of the melittin family of proteins, which are known for their ability to disrupt cell membranes. Styloidiin is a 26-amino acid peptide that is highly cationic, meaning it carries a positive charge. This charge allows it to bind to the negatively charged phospholipids in cell membranes, causing them to become permeable and leading to cell lysis.

Styloidiin has been studied for its potential therapeutic applications, particularly in the treatment of cancer. Its ability to disrupt cell membranes makes it a potent cytotoxic agent, capable of inducing apoptosis in cancer cells. However, its use is limited by its high toxicity to normal cells, which can lead to significant side effects.

The structure of styloidiin has been determined using X-ray crystallography, revealing a compact, alpha-helical structure. The positively charged amino acids in the peptide are concentrated on one face of the helix, which is thought to facilitate its interaction with cell membranes.

Styloidiin is not the only melittin-like peptide found in the venom of Melissodes styloides. Other peptides, such as melittin and apamin, are also present and contribute to the venom's overall toxicity. The venom of Melissodes styloides is highly toxic to humans, with a median lethal dose (LD50) of approximately 0.05 mg/kg in mice. This toxicity is due to the combined effects of the various peptides in the venom, including styloidiin.