Origins of Helix−Coil Switching in a Light-Sensitive Peptide

Abstract

Intramolecular cross-linking of peptides by the light-sensitive compound diiodoacetamideazobenzene has been shown to permit reversible photocontrol of the helix-coil transition. Cross-linking between Cys residues spaced at i and i + 7 positions with the trans form of the linker was found to produce a decreased helix content compared to that of the non-cross-linked peptide. Photoisomerization to the cis form of the linker led to substantially higher helix content than in the non-cross-linked peptide. Detailed conformational analysis of the system leads to the conclusion that photocontrol of helix content does not involve specific interactions between the linker and the peptide. Instead, the change in peptide helix content caused by photoisomerization can be predicted by comparing the length ranges of the cis and trans forms of the linker with the expected distance distribution of the Cys attachment points in the intrinsic conformational ensemble of the peptide. The analysis presented here should help to guide the use of these and related linkers for the conformational control of a variety of peptide and protein systems.

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

“…The extent to which this is achieved depends critically on where the switch is placed and how well isomerization is coupled to protein conformational change. Incorrect placement can lead to inconsequential changes in conformation or to switches becoming locked in the cis or trans state [15][16][17] .…”

“…We have focused primarily on targeting the conformational control of helical structures using thiol-reactive, azobenzenebased photo-switchable cross-linkers 3,16,20,21 . As Cys residues can easily be introduced via site-directed mutagenesis, this azobenzenebased cross-linking strategy offers a fairly general way to photocontrol protein a-helix content and thereby activity.…”

Spectral Tuning of Azobenzene Photoswitches for Biological Applications

“…The peptide JRK-W, a model helix-forming peptide that has been studied extensively, [19] was intramolecularly cross-linked with the chloroacetyl derivative of 5 f, as shown in Figure 2. As expected, based on previous work with the parent cross-linker [19] the trans isomer destabilized the JRK-W helix. Irradiation with a 400-nm LED produced about 50 % cis isomer and a substantial increase in helix content as judged by circular dichroism spectrometry (Figure 2).…”

Synthesis and Characterization of a Long, Rigid Photoswitchable Cross‐Linker for Promoting Peptide and Protein Conformational Change

“…The minimum A C H T U N G T R E N N U N G distance change is 6 , almost double that of the BSBCA crosslinker. [23] We then designed two test peptide sequences with Cys residues spaced to match either the trans or cis form of the crosslinker. Both peptide sequences are derived from the general , [33,34] which is helical and monomeric in aqueous solution.…”

“…For example, with the amide-functionalized azobenzene, 3,3'-bis(sulfonato)-4,4'-bis(chloroacetamide)azobenzene (BSBCA), the end-to-end distance distribution was 11-15 for the cis form and 19-23 for the trans form so that a minimum end-to-end distance change of only~4 is still possible. [23] Moroder and colleagues recently introduced an azobenzenebased cross-linker bearing rigid alkyne units at each end that was successfully used to photocontrol the conformation of collagen peptide sequences. [24,25] The alkyne units significantly extend the length of the cross-linker, but the presence of sp 3 -hybridized carbon atoms on either side of the alkyne can also permit flexibility that mutes end-to-end distance changes produced.…”