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author:("Shi, wenchuan")
1.  Selective Membrane Disruption: Mode of Action of C16G2, a Specifically Targeted Antimicrobial Peptide ▿ 
The specifically targeted antimicrobial peptide (STAMP) C16G2 was developed to target the cariogenic oral pathogen Streptococcus mutans. Because the design of this peptide was novel, we sought to better understand the mechanism through which it functioned. Compared to antimicrobial peptides (AMPs) with wide spectra of activity, the STAMP C16G2 has demonstrated specificity for S. mutans in a mixed-culture environment, resulting in the complete killing of S. mutans while having minimal effect on the other streptococci. In the current study, we sought to further confirm the selectivity of C16G2 and also compare its membrane activity to that of melittin B, a classical toxic AMP, in order to determine the STAMP's mechanism of cell killing. Disruption of S. mutans cell membranes by C16G2 was demonstrated by increased SYTOX green uptake and ATP efflux from the cells similar to those of melittin B. Treatment with C16G2 also resulted in a loss of membrane potential as measured by DiSC(3)5 fluorescence. In comparison, the individual moieties of C16G2 demonstrated no specificity and limited antimicrobial activity compared to those of the STAMP C16G2. The data suggest that C16G2 has a mechanism of action similar to that of traditional AMPs and kills S. mutans through disruption of the cell membrane, allowing small molecules to leak out of the cell, which is followed by a loss of membrane potential and cell death. Interestingly, this membrane activity is rapid and potent against S. mutans, but not other noncariogenic oral streptococci.
doi:10.1128/AAC.00342-11
PMCID: PMC3122425  PMID: 21518845
2.  Systematic Approach to Optimizing Specifically Targeted Antimicrobial Peptides against Streptococcus mutans▿  
Previously we reported a novel strategy of “targeted killing” through the design of narrow-spectrum molecules known as specifically targeted antimicrobial peptides (STAMPs) (R. Eckert et al., Antimicrob. Agents Chemother. 50:3651-3657, 2006; R. Eckert et al., Antimicrob. Agents Chemother. 50:1480-1488, 2006). Construction of these molecules requires the identification and the subsequent utilization of two conjoined yet functionally independent peptide components: the targeting and killing regions. In this study, we sought to design and synthesize a large number of STAMPs targeting Streptococcus mutans, the primary etiologic agent of human dental caries, in order to identify candidate peptides with increased killing speed and selectivity compared with their unmodified precursor antimicrobial peptides (AMPs). We hypothesized that a combinatorial approach, utilizing a set number of AMP, targeting, and linker regions, would be an effective method for the identification of STAMPs with the desired level of activity. STAMPs composed of the Sm6 S. mutans binding peptide and the PL-135 AMP displayed selectivity at MICs after incubation for 18 to 24 h. A STAMP where PL-135 was replaced by the B-33 killing domain exhibited both selectivity and rapid killing within 1 min of exposure and displayed activity against multispecies biofilms grown in the presence of saliva. These results suggest that potent and selective STAMP molecules can be designed and improved via a tunable “building-block” approach.
doi:10.1128/AAC.01391-09
PMCID: PMC2863653  PMID: 20211885
3.  Novel Synthetic Antimicrobial Peptides against Streptococcus mutans▿  
Streptococcus mutans, a common oral pathogen and the causative agent of dental caries, has persisted and even thrived on the tooth surface despite constant removal and eradication efforts. In this study, we generated a number of synthetic antimicrobial peptides against this bacterium via construction and screening of several structurally diverse peptide libraries where the hydrophobicity and charge within each library was varied incrementally in order to generate a collection of peptides with different biochemical characteristics. From these libraries, we identified multiple peptides with robust killing activity against S. mutans. To further improve their effectiveness, the most bactericidal peptides from each library were synthesized together as one molecule, in various combinations, with and without a flexible peptide linker between each antimicrobial region. Many of these “fusion” peptides had enhanced killing activities in comparison with those of the original nonconjoined molecules. The results presented here illustrate that small libraries of biochemically constrained peptides can be used to generate antimicrobial peptides against S. mutans, several of which may be likely candidates for the development of anticaries agents.
doi:10.1128/AAC.01270-06
PMCID: PMC1855471  PMID: 17296741
4.  Enhancement of Antimicrobial Activity against Pseudomonas aeruginosa by Coadministration of G10KHc and Tobramycin▿  
Antimicrobial Agents and Chemotherapy  2006;50(11):3833-3838.
Pseudomonas aeruginosa is a common opportunistic human pathogen that is associated with life-threatening acute infections and chronic airway colonization during cystic fibrosis. Previously, we converted the wide-spectrum antimicrobial peptide novispirin G10 into a selectively-targeted antimicrobial peptide (STAMP), G10KHc. Compared to novispirin G10, the STAMP had an enhanced ability to kill Pseudomonas mendocina. In this study, we explored the activity of G10KHc against P. aeruginosa. G10KHc was found to be highly active (as active as tobramycin) against P. aeruginosa clinical isolates. Most interestingly, we observed a synergistic-like enhancement in killing activity when biofilms and planktonic cultures of P. aeruginosa were cotreated with G10KHc and tobramycin. The data indicate that the mechanism of enhanced activity may involve increased tobramycin uptake due to G10KHc-mediated cell membrane disruption. These results suggest that G10KHc may be useful against P. aeruginosa during acute and chronic infection states, especially when it is coadministered with tobramycin.
doi:10.1128/AAC.00509-06
PMCID: PMC1635211  PMID: 16940063
5.  Targeted Killing of Streptococcus mutans by a Pheromone-Guided “Smart” Antimicrobial Peptide 
Antimicrobial Agents and Chemotherapy  2006;50(11):3651-3657.
Within the repertoire of antibiotics available to a prescribing clinician, the majority affect a broad range of microorganisms, including the normal flora. The ecological disruption resulting from antibiotic treatment frequently results in secondary infections or other negative clinical consequences. To address this problem, our laboratory has recently developed a new class of pathogen-selective molecules, called specifically (or selectively) targeted antimicrobial peptides (STAMPs), based on the fusion of a species-specific targeting peptide domain with a wide-spectrum antimicrobial peptide domain. In the current study, we focused on achieving targeted killing of Streptococcus mutans, a cavity-causing bacterium that resides in a multispecies microbial community (dental plaque). In particular, we explored the possibility of utilizing a pheromone produced by S. mutans, namely, the competence stimulating peptide (CSP), as a STAMP targeting domain to mediate S. mutans-specific delivery of an antimicrobial peptide domain. We discovered that STAMPs constructed with peptides derived from CSP were potent against S. mutans grown in liquid or biofilm states but did not affect other oral streptococci tested. Further studies showed that an 8-amino-acid region within the CSP sequence is sufficient for targeted delivery of the antimicrobial peptide domain to S. mutans. The STAMPs presented here are capable of eliminating S. mutans from multispecies biofilms without affecting closely related noncariogenic oral streptococci, indicating the potential of these molecules to be developed into “probiotic” antibiotics which could selectively eliminate pathogens while preserving the protective benefits of a healthy normal flora.
doi:10.1128/AAC.00622-06
PMCID: PMC1635210  PMID: 17060534
6.  Adding Selectivity to Antimicrobial Peptides: Rational Design of a Multidomain Peptide against Pseudomonas spp. 
Currently available antimicrobials exhibit broad killing with regard to bacterial genera and species. Indiscriminate killing of microbes by these conventional antibiotics can disrupt the ecological balance of the indigenous microbial flora, often resulting in negative clinical consequences. Species-specific antimicrobials capable of precisely targeting pathogenic bacteria without damaging benign microorganisms provide a means of avoiding this problem. In this communication, we report the successful creation of the first synthetic, target-specific antimicrobial peptide, G10KHc, via addition of a rationally designed Pseudomonas-specific targeting moiety (KH) to a generally killing peptide (novispirin G10). The resulting chimeric peptide showed enhanced bactericidal activity and faster killing kinetics against Pseudomonas spp. than G10 alone. The enhanced killing activities are due to increased binding and penetration of the outer membrane of Pseudomonas sp. cells. These properties were not observed in tests of untargeted bacterial species, and this specificity allowed G10KHc to selectively eliminate Pseudomonas spp. from mixed cultures. This work lays a foundation for generating target-specific “smart” antimicrobials to complement currently available conventional antibiotics.
doi:10.1128/AAC.50.4.1480-1488.2006
PMCID: PMC1426969  PMID: 16569868

Results 1-6 (6)