Relationship between Hydrophobic Interactions and Secondary Structure Stability for Trpzip β-Hairpin Peptides

Abstract

The temperature-induced beta-hairpin stabilities of selected mutations of the Trpzip1 peptide, SWTWEGNKWTWK (WWWW), have been investigated by electronic circular dichroism (CD), Raman, and FT-IR spectroscopies. The tryptophan (Trp) residues in the original Trpzip1 sequence were systematically substituted with tyrosine (Tyr) in different positions to test the impact of Trp interactions on the beta-hairpin structure and stability. The CD intensity at approximately 228 nm, which arises from Trp-Trp interactions (tertiary structure), and the amide I' IR absorbance at approximately 1635 cm(-1) (secondary structure) have been measured over a range of temperatures to investigate the impact of Tyr substitution on beta-hairpin thermal stability in Trpzip peptides. Mutation from Trp to Tyr in the Trpzip1 sequence reduces the extent of beta-hairpin structure and monotonically decreases the beta-hairpin stability of Trpzip1 mutant peptides with an increasing number of Tyr substitutions. Substituted Trpzip peptides with just one pair of Trp-Trp interactions close to either the terminal residues (WYYW) or the turn (YWWY) have similar stabilities. Comparison of conformational transitions monitored by CD and IR reveals them to have multistate behavior in which the temperature-induced disruption of the Trp-Trp interaction (tertiary structure) occurs at a lower temperature than the unfolding of the secondary structure.

Antimicrobial activity and membrane-active mechanism of tryptophan zipper-like β-hairpin antimicrobial peptides

“…CD study shows that this peptide exists primarily as a β-hairpin in aqueous buffer. HB hydrogenbonded site, NHB non-hydrogen-bonded site in PBS, the CD spectra of the designed peptides closely match the CD curves of those fully folded tryptophan zippers in shape and are indicative of well-formed β-hairpin structures (Cochran et al 2001;Dong et al 2006;Takekiyo et al 2009). The minimum at ∼214 nm is consistent with β-sheet structure (Riemen and Waters 2009), and the characteristic maximum at ~228 nm due to the π-π* exciton coupling originating from the interacting Trp residues is indicative of a distinctive cross-strand Trp-Trp interaction ).…”

“…Some of the most stable β-hairpin peptides designed to date are tryptophan zipper (trpzip) peptides, which are linear peptides containing one or two Trp-Trp cross-strand pairs at non-hydrogen-bonded sites (Cochran et al 2001;Eidenschink et al 2009;Santiveri et al 2011;Takekiyo et al 2009;Wu et al 2012). These peptides are among the shortest β-hairpin peptides known to fold spontaneously without requiring disulfide crosslinks or metal binding.…”

Cross-Strand Coupling and Site-Specific Unfolding Thermodynamics of a Trpzip β-Hairpin Peptide Using 13C Isotopic Labeling and IR Spectroscopy

“…In the far-UV region, these peptides have a negative (∼213 nm), then positive (∼227 nm), couplet band, which arises from exciton coupling of tryptophan residues on opposite strands. [70][71][72] These bands indicate that there are electronic coupling (exciton) interactions between residues Trp2-Trp11 and Trp4-Trp9, where they are arranged in an edge-toface geometry. Our TD-DFT calculations support this interpretation (see Discussion and Supporting Information).…”

Impact of β‐Turn Sequence on β‐Hairpin Dynamics Studied with Infrared‐Detected Temperature Jump

“…Trpzip molecules at low temperatures have characteristic β-structure IR which reverts to a disordered structure spectrum at higher temperatures [16,17,[22][23][24]. We have separately reported equilibrium studies of various modifications of the Trpzip2 (TZ2-NG) hairpin sequence Ser-Trp-Thr-Trp-GluAsn-Gly-Lys-Trp-Thr-Trp-Lys (SWTWENGKWTWK) [8], varying both the Trps and the turn sequence residues [13,14,16,17,25,26]. We and others have also used laser-initiated T-jump spectroscopy to study dynamics of the TZ2-NG sequence and have incorporated isotopic labels to specify sequence dependence of the folding mechanism [17,27,28].…”