Single-molecule mechanical unfolding experiments reveal a critical length for the formation of α-helices in peptides

Abstract

α-helices in peptide sequences made of more than 20 amino acid residues selffold in a structure made of short helices instead of an intact compact helix.

Side chain interactions govern the response of polypeptide alpha-helices under mechanical stress and prevent the formation of beta-sheets

“…The most stable and thermodynamically favoured length of a single a-helix was shown to be below 20 amino acids. 16,24 While this suggests that we should detect the mechanical unfolding of several helices of 20 residues, only one plateau is observed in the force curves and not a series of consecutive plateaus. We have shown recently 16 that when the cantilever displacement begins to align the whole molecule backbone in the pulling direction, the higher order structure is lost as the separated a-helix segments align on top of each other.…”

“…We previously showed that this approach, based on the physisorption of caught PEG tethers onto the tip, provides a sufficiently strong and stable attachment of the molecule onto the tip to obtain reliable information on the system grafted on the surface. [14][15][16][17][18][19] As a result of the different side chains (Figure 1), the ahelices form under opposite pH conditions, pH > 11 for PLys and pH < 4 for PGA. Immediately prior to performing single-molecule force spectroscopy experiments, the gold substrates were dipped in a diluted solution of the molecules and a passivating agent PEG6-SH was added, to enable single molecules to be individually distributed and immobilized onto the cleaned surface (see Methods section).…”

“…This approach, combined with the small size of the molecules, also prevents the unspecific adsorption of the polymer chains onto the surface and gives rise to very clean force curves without unspecific peaks. 14,16,[18][19][20][21] Poly(L-lysine) mechanical unfolding. The typical forceextension profile for PLys in a-helix conformation at pH 12 shows a plateau at 34 ± 4 pN (Figure 2).…”

Stimuli-responsive Molecular Springs Based on Single- and Multi-stranded Helical Structures

“…However, little is known about the ability of the helix-based molecular springs to convert their conformational changes into a force and to produce actual work. The results for single molecule force spectroscopic studies on the unfolding and refolding processes of biopolymers, such as double helical DNA and α-helical peptides, 100,101 may help to design helix-based molecular systems with such functions. The microscopic springlike motion if amplified to express the molecular motions to perform work on a macroscopic scale, as demonstrated with great interest by the lifting performance of a U.S. dime using self-organizable thermoresponsive helical poly(phenylacetylene)s by Percec et al, 89,94 will move a step closer to the developments of molecular machine-based smart materials capable of working in real life.…”

Drug Discovery Targeting the Disorder-To-Order Transition Regions through the Conformational Diversity Mimicking and Statistical Analysis

“…For mimicking characteristics of intrinsically disordered region, we obtained diverse structures of target disorder-to-order transition region after its segmentation into a set of overlapping 20-amino-acid-long peptides. This length of segmentation was used because a 20-amino-acid-long peptide is optimal for the unfolding and folding studies [ 25 ]. We segmented protein sequences into subsets ( Table 1 ) and then uploaded them on PEPFOLD v3.5 web server ( ) to predict peptide structures [ 16 ].…”