Cecropin Peptides

Definition
Cercopins are antimicrobial peptides that are part of immune response of silkworm1.

Discovery
Cercopins were first isolated from the silkworm Hyalophora cecropia in 19812.

Classification
Cercopins are of three types, A, B and C which range from 35-38 amino acids in length1.

Structural Characteristics
Cercopin has a helix bend helix motif. Its N-terminus is positively charged and amphipatic in nature1. The C terminus is less charged and hydrophobic1. The hinge between the helices is formed by amino acids Gly 23 and Pro 241.

Mode of action
The amino terminal helix binds to the negative charged head groups on the cell membrane and the hydrophobic residues of the C terminus insert into the membrane core3. Then application of a positive potential pushes the NH2 terminal into the membrane to form pores thus killing the microorganism3.

Functions
Cercopins apart from killing bacteria permeabilize liposomes1. In vitro they are effective against plant pathogenic bacteria1.

References
1.Durell SR, Raghunathan G, Guy HR (1992). Modeling the ion channel structure of cecropin, Biophys J, 63(6), 1623-31.
2.Steiner H, Hultmark D, Engström A, Bennich H, Boman HG (1981). Sequence and specificity of two antibacterial proteins involved in insect immunity, Nature, 292(5820), 246-8.
3.Vaara M and Vaara T (1994). Ability of Cecropin B To Penetrate the Enterobacterial
Outer Membrane, Antimicrobial agents and Chemotherapy,38, 2498-2501.