Using an Azobenzene Cross-Linker to Either Increase or Decrease Peptide Helix Content upon Trans-to-Cis Photoisomerization

Abstract

Reversible photocontrol of peptide and protein conformation could prove to be a powerful tool for probing function in diverse biological systems. Here, we report reversible photoswitching of the helix content in short peptides containing an azobenzene cross-linker between cysteine residues at positions i, i + 4, or i, i + 11 in the sequence. Trans-to-cis photoisomerization significantly increases the helix content in the i, i + 4 case and significantly decreases the helix content in the i, i + 11 case. These cross-linker designs significantly expand the possibilities for photocontrol of peptide and protein structure.

Synthesis of 3,3′-bis(sulfonato)-4,4′-bis(chloroacetamido)azobenzene and cysteine cross-linking for photo-control of protein conformation and activity

“…A variety of helical peptides and proteins bearing two Cys residues have been cross-linked, and their conformational and functional properties have been studied; these include the peptides JRK-7 and FK-11 and the proteins MyoD, engrailed and GCN4 27,[29][30][31] . Intermolecular cross-linking between proteins was not apparent in any of these cases and was likely suppressed by the fast intramolecular reaction between the chloroacetamide moiety of BSBCA and the second Cys residue.…”

“…(iii) To date, the effects of BSBCA on helical structures alone have been characterized. When Cys residues spaced i, i+4 or i, i+7 are cross-linked, trans-to-cis isomerization of the linker can promote helix formation, but when Cys residues spaced i, i+11 are cross-linked, trans-to-cis isomerization of the linker inhibits helix formation 27 . The extent of regulation of the helix structure depends on the energetics and dynamics of conformational changes in each particular case.…”

Two-Dimensional Infrared Spectroscopy of Photoswitchable Peptides

“…It is characterized by a high quantum yield (50%), high photostability, ultrafast switching speed (approximately 1 ps), and the fact that cis and trans isomers have absorption bands that are well separated, therefore allowing a selective switching in both directions (107). Various groups (108)(109)(110)(111)(112)(113)(114)(115)(116)(117)(118)(119)(120)(121) Photoswitchable peptides and intrinsic photoswitches studied in our lab: azobenzene (a) embedded into a peptide backbone (b) or cross-linking amino acid side chains, and (c) a photocleavable disulfide bridge and (d ) thiopeptides.…”

“…The change of homogeneous width during the diffusion-controlled phase revealed by T2D-IR may reflect the width of the conformation space accessible on a fast timescale, which becomes more confined as the backbone approaches its global energy minimum. In ongoing work, we concentrate on an alternative approach designed by Woolley and coworkers (110,(113)(114)(115), who used an azobenzene moiety to cross-link two amino acid side chains of a polypeptide (Figure 4b). Depending on its end-to-end distance, the photoswitch either increases or decreases the helix propensity of the peptide upon cis-trans isomerization (110,(113)(114)(115).…”

“…In ongoing work, we concentrate on an alternative approach designed by Woolley and coworkers (110,(113)(114)(115), who used an azobenzene moiety to cross-link two amino acid side chains of a polypeptide (Figure 4b). Depending on its end-to-end distance, the photoswitch either increases or decreases the helix propensity of the peptide upon cis-trans isomerization (110,(113)(114)(115). However, in contrast to the previous example, the photoswitch couples much less directly to the conformational transition of the peptide backbone.…”