Biological nanopores for single-molecule sensing.

Evolution has found countless ways to transport material across cells and cellular compartments separated by membranes. Protein assemblies are the cornerstone for the formation of channels and pores that enable this regulated passage of molecules in and out of cells, contributing to maintaining most of the fundamental processes that sustain living organisms. As in several other occasions, we have borrowed from the natural properties of these biological systems to push technology forward and have been able to hijack these nano-scale proteinaceous pores to learn about the physical and chemical features of molecules passing through them.

Targeting specific membranes with an azide derivative of the pore-forming peptide ceratotoxin A.

Pore-forming antimicrobial peptides (AMPs) are attracting interest as cytolytic antibiotics and drug delivery agents with potential use for targeting cancer cells or multidrug-resistant pathogens. Ceratotoxin A (CtxA) is an insect-derived cytolytic AMP with 36 amino acids that is thought to protect the eggs of the medfly Ceratitis capitata against pathogens. Single channel recordings using planar lipid bilayers have shown that CtxA forms pores with well-defined conductance states resembling those of alamethicin; it also forms one of the largest pores among the group of ceratotoxins.

Single channel planar lipid bilayer recordings of the melittin variant MelP5.

MelP5 is a 26 amino acid peptide derived from melittin, the main active constituent of bee venom, with five amino acid replacements. The pore-forming activity of MelP5 in lipid membranes is attracting attention because MelP5 forms larger pores and induces dye leakage through liposome membranes at a lower concentration than melittin. Studies of MelP5 have so far focused on ensemble measurements of membrane leakage and impedance; here we extend this characterization with an electrophysiological comparison between MelP5 and melittin using planar lipid bilayer recordings.