The π Configuration of the WWW Motif of a Short Trp-Rich Peptide Is Critical for Targeting Bacterial Membranes, Disrupting Preformed Biofilms, and Killing Methicillin-Resistant <i>Staphylococcus aureus</i>

Tryptophan-rich peptides, being short and suitable for large-scale chemical synthesis, are attractive candidates for developing a new generation of antimicrobials to combat antibiotic-resistant bacteria (superbugs). Although there are numerous pictures of the membrane-bound structure of a single tryptophan (W), how multiple Trp amino acids assemble themselves and interact with bacterial membranes is poorly understood. This communication presents the three-dimensional structure of an eight-residue Trp-rich peptide (WWW­L­R­KIW-NH₂ with 50% W) determined by the improved two-dimensional nuclear magnetic resonance method, which includes the measurements of ¹³C and ¹⁵N chemical shifts at natural abundance. This peptide forms the shortest two-turn helix with a distinct amphipathic feature. A unique structural arrangement is identified for the Trp triplet, WWW, that forms a π configuration with W2 as the horizontal bar and W1/W3 forming the two legs. An arginine scan reveals that the WWW motif is essential for killing methicillin-resistant <i>Staphylococcus aureus</i> USA300 and disrupting preformed bacterial biofilms. This unique π configuration for the WWW motif is stabilized by aromatic–aromatic interactions as evidenced by ring current shifts as well as nuclear Overhauser effects. Because the WWW motif is maintained, a change of I7 to R led to a potent antimicrobial and antibiofilm peptide with 4-fold improvement in cell selectivity. Collectively, this study elucidated the structural basis of antibiofilm activity of the peptide, identified a better peptide candidate via structure–activity relationship studies, and laid the foundation for engineering future antibiotics based on the WWW motif

Additional file 1 of The pathogenicity of vancomycin-resistant Enterococcus faecalis to colon cancer cells

Supplementary Material 1

Synthesis of Novel Fluorescent Cellulose Derivatives and Their Applications in Detection of Nitroaromatic Compounds

A series of fluorescent cellulose derivatives (AC-AET-DMANMs) with different degrees of substitution (DS) were successfully prepared. First, allyl cellulose (AC) was synthesized from cellulose in NaOH/urea aqueous solution, and then 2-aminoethanethiol (AET) was introduced onto the cellulose backbone via a thiol–ene click reaction. Finally, the fluorescent groups were introduced by the reaction of the AET-modified AC with 4-dimethylamine-1,8-naphthalic anhydride (DMANA). The structure and fluorescent properties of AC-AET-DMANMs were characterized by elemental analysis and FT-IR, ¹H NMR, UV–vis, and fluorescence spectroscopy. AC-AET-DMANM with lower DS_DMANM (referring to the DS of naphthalimide groups, ≤0.25) was soluble in DMSO. AC-AET-DMANM of DS_DMANM ≤ 0.09 displayed stable fluorescence in DMSO and even in the solid state. The emission of AC-AET-DMANM in DMSO quantitatively and sensitively responded to 2,4,6-trinitrophenol (TNP) and 2,4-dinitrophenylhydrazine (DNH) by fluorescence quenching, and the limits of detection were determined to be 1.4 × 10^–7 and 9.9 × 10^–8 mol/L, respectively. Moreover, a water-soluble fluorescent derivative (AC-AET-DMANM-2W) was prepared by a further thiol–ene click reaction between AC-AET-DMANM-2 and AET. It can also be applied in the detection of TNP and DNH in aqueous media with the detection limits of 2.5 × 10^–8 and 3.2 × 10^–8 mol/L, respectively. The quenching mechanism is attributed to the photoinduced electron transfer and resonance energy transfer of the fluorescent cellulose derivatives to TNP/DNH molecules. The results illustrate a high applicability of the novel fluorescent cellulose derivatives to the detection of specific chemical entities in aqueous/nonaqueous media