Melittin is the main component (40–60% of the dry weight) and the major pain-producing substance of honeybee (Apis mellifera) venom. Melittin is a basic peptide consisting of 26 amino acids.
Function
The principal function of melittin as a component of bee venom is to cause pain and destruction of tissue of intruders that threaten a beehive. However, melittin is expressed, not only in the venom gland, but also in other tissues when the bee is infected with various pathogens. The over-expression of melittin (as well as secapin, another venom molecule) in infected honey bees may indicate that it plays a role in the immune response of bees to infectious diseases.
Structure
Melittin is a small peptide with no disulfide bridge; the N-terminal part of the molecule is predominantly hydrophobic and the C-terminal part is hydrophilic and strongly basic. In water, it forms a tetramer, but it also can spontaneously integrate itself into cell membranes.
Mechanism of action
Injection of melittin into animals and humans causes pain sensations. It has strong surface effects on cell membranes, causing pore formation in epithelial cells and the destruction of red blood cells. Melittin also activates nociceptor (pain receptor) cells through a variety of mechanisms. At the sites of multiple stings, localized pain, swelling, and skin redness occur, and if bees are swallowed, life-threatening swelling of the throat and respiratory passages may develop.
Gallery
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File:"Melittin" from the series "The Building Blocks of Life".jpg|Steel sculpture based on the structure of melittin by Julian Voss-Andreae
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