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author:("Shi, wenchuan")
1.  PilA localization affects extracellular polysaccharide production and fruiting body formation in Myxococcus xanthus 
Molecular microbiology  2010;76(6):1500-1513.
Summary
Myxococcus xanthus is a gram-negative bacterium capable of complex developmental processes involving vegetative swarming and fruiting body formation. Social (S-) gliding motility, one of the two motility systems employed by M. xanthus, requires at least two cell surface structures: type IV pili (TFP) and extracellular polysaccharides (EPS). Extended TFP which are composed of thousands of copies of PilA retract upon binding to EPS and thereby pull the cell forward. TFP also act as external sensor to regulate EPS production. In this study, we generated a random PilA mutant library and identified one derivative, SW1066, which completely failed to undergo developmental processes. Detailed characterization revealed that SW1066 produced very little EPS but wild-type amounts of PilA. These mutated PilA subunits, however, are unable to assemble into functional TFP despite their ability to localize to the membrane. By preventing the mutated PilA of SW1066 to translocate from the cytoplasm to the membrane, fruiting body formation and EPS production was restored to the levels observed in mutant strains lacking PilA. This apparent connection between PilA membrane accumulation and reduction in surface EPS implies that specific cellular PilA localization are required to maintain the EPS level necessary to sustain normal S-motilityin M. xanthus.
doi:10.1111/j.1365-2958.2010.07180.x
PMCID: PMC2935901  PMID: 20444090
Myxococcus xanthus; type four pili; PilA; extracellular polysaccharide
2.  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

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