The capture of single strands of DNA inside the α‐hemolysin (α‐HL) transmembrane pore protein upon application of a positive potential leads to single α‐HL⋅DNA pseudorotaxane species (see picture). By monitoring the characteristic decreases in the ion conductance of α‐HL, a single adenine nucleotide can be identified at a specific location on a strand of DNA.

Cyclic peptides with an even number of alternating D,L-␣-amino acid residues are known to self-assemble into organic nanotubes. Such peptides previously have been shown to be stable upon protease treatment, membrane active, and bactericidal and to exert antimicrobial activity against Staphylococcus aureus and other gram-positive bacteria. The present report describes the in vitro and in vivo pharmacology of selected members of this cyclic peptide family. The intravenous (i.v.) efficacy of six compounds with MICs of less than 12 g/ml was tested in peritonitis and neutropenic-mouse thigh infection models. Four of the six peptides were efficacious in vivo, with 50% effective doses in the peritonitis model ranging between 4.0 and 6.7 mg/kg against methicillin-sensitive S. aureus (MSSA). In the thigh infection model, the four peptides reduced the bacterial load 2.1 to 3.0 log units following administration of an 8-mg/kg i.v. dose. Activity against methicillin-resistant S. aureus was similar to MSSA. The murine pharmacokinetic profile of each compound was determined following i.v. bolus injection. Interestingly, those compounds with poor efficacy in vivo displayed a significantly lower maximum concentration of the drug in serum and a higher volume of distribution at steady state than compounds with good therapeutic properties. S. aureus was unable to easily develop spontaneous resistance upon prolonged exposure to the peptides at sublethal concentrations, in agreement with the proposed interaction with multiple components of the bacterial membrane canopy. Although additional structure-activity relationship studies are required to improve the therapeutic window of this class of antimicrobial peptides, our results suggest that these amphipathic cyclic D,L-␣-peptides have potential for systemic administration and treatment of otherwise antibiotic-resistant infections.The incidence of community-acquired and nosocomially acquired infections due to the bacterium Staphylococcus aureus is rising (25). From 1990 to 1992, this microorganism was the most common cause of nosocomial pneumonias and surgical wound infections (14). The overall growing crisis in antibiotic resistance and the rise in the incidence of methicillin-resistant S. aureus (MRSA) strains (32, 33) have emphasized the need for therapeutic alternatives to currently available antibiotics. Vancomycin remains the mainstay of therapy against several resistant gram-positive pathogens. However, vancomycin is slowly bactericidal, and with the recent increase in nosocomial infections caused by vancomycin-resistant enterococci and S. aureus (4, 13, 16), there is a growing need for antimicrobial agents with novel mechanisms of action to attack these resistant pathogens. The Food and Drug Administration recently approved the use of daptomycin, a cyclic lipodepsipeptide antibiotic, for the treatment of complicated skin and skin structure infections caused by several gram-positive bacteria. Its mode of action seems to be related to the disruption of the membrane potential of ...

No abstract

A selective heteromeric supramolecular assembly process is devised to create functional single channels of altered ion conductance, charge selectivity, and rectification. The hollow transmembrane tubular structure produced spontaneously from the self-assembly of cyclic-d,l-alpha-peptides in lipid bilayers is modified by designer cyclic peptide "cap" subunits that bind site-selectively at the mouth of the channel assembly.

Recently, cyclodextrins were shown to act as adapters for the pore-forming protein staphylococcal α-hemolysin (αHL). The bagel-shaped molecules bind in the lumen of the transmembrane channel formed by αHL and alter the properties of the pore. For example, the unitary conductance is reduced, and organic molecules can act as channel blockers by binding to the cavity within the cyclodextrin adapter. In a search for a class of adapters more versatile than the cyclodextrins and amenable to preparation as libraries, cyclic peptides have now been examined. Four peptides, cyclo[(l-Arg-d-Leu)4-] ((RL)4), cyclo[(l-Glu-d-Leu)4-] ((EL)4), cyclo[(-l-Phe-d-N-(aminoethyl)-Ala-l-Phe-d-Ala)2-] (diNH3 +-(FA)4), and cyclo[(-l-Phe-d-N-(carboxymethyl)-Ala-l-Phe-d-Ala)2-] (diCO2 --(FA)4), became lodged within the αHL pore, altering the unitary conductance and ion selectivity. Further, the positively charged peptides, (RL)4 and diNH3 +-(FA)4, were able to act as binding sites for various small polyanions. For example, the second messenger IP3 bound to (RL)4 within the αHL pore. Therefore, the modulation of single-channel currents through pores containing cyclic peptide adapters may prove useful for sensing a variety of molecules.