| Symbol: | Melittin |
| Melittin | |
| Pfam: | PF01372 |
| Interpro: | IPR002116 |
| Scop: | 2mlt |
| Tcdb: | 1.C.18 |
| Opm Family: | 151 |
| Opm Protein: | 2mlt |
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.[1]
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, in honey bees, melittin is not only expressed in the venom gland, but also in other tissues when infected with pathogens. The two venom molecules, melittin and secapin, that are over-expressed in honey bees infected with various pathogens, possibly indicate a role for melittin in the immune response of bees to infectious diseases.[2]
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.[3]
Injection of melittin into animals and humans causes pain sensation. 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.
Melittin can open thermal nociceptor TRPV1 channels via cyclooxygenase metabolites resulting in depolarization of nociceptor cells. The pore forming effects in cells causes the release of pro-inflammatory cytokines. It also activates G-protein-coupled receptor-mediated opening of transient receptor potential channels. Finally melittin up-regulates the expression of Nav1.8 and Nav1.9 sodium channels in nociceptor cell causing long term action potential firing and pain sensation.
Melittin inhibits protein kinase C, Ca2+/calmodulin-dependent protein kinase II, myosin light chain kinase, and Na+/K+-ATPase (synaptosomal membrane). Melittin blocks transport pumps such as the Na+-K+-ATPase and the H+-K+-ATPase.
See also: Bee sting. Melittin is the main compound in bee venom, accounting for the potential lethality of a bee sting, which causes an anaphylactic reaction in some people.[4] 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.[4]
Bee venom therapy has been used in traditional medicine for treating various disorders,[5] although its non-specific toxicity has limited scientific research on its potential effects.[6]