Types of Interactions

In solution, mostly intramolecular interactions as listed in Fig. 13.1 dominate folding. Among the most important conformational equilibria is the coil-helix transition (Fig. 13.2), where intrachain contacts stabilize the helical conformation. Above a critical concentration, intermolecular interactions become important and aggregation can also affect secondary structure formation (see Chapter 4), as illustrated in the formation of b-sheets held together by interchain contacts (Fig. 13.2). At...

S03

Fig. 8.14 Major repeat of heparin and a heparin binding aryl amide. Backbone rigidifying H-bonds are shown as dashed lines. inhibitory effect on cholesterol uptake in either model. On the other hand, while none of the previously tested a-peptide inhibitors induced effects in whole CaCO-2 cells, a b-peptide nonamer decreased the absorption rate of radiolabeled cholesterol to background levels (indicated by an increase in T1 2 of cholesterol absorption rate from 102 min to 2.6 h). This suggested...

N R H 27n R CH3 n 8 10 12 14 16

Functionalization of the helix interior can influence binding strength and selectivity. With internal cyano groups, mPE foldamers could bind metal ions such as Ag(I) 124 . Oligo(m-ethynylpyridine) was shown by Inouye and colleagues to fold in the presence of certain monosaccharides 125 . The state of ionization was found later to strongly influence the propensity of these oligomers to bind saccharides and fold 126 . Details can be found in Chapter 7 of this book. Folding is not limited to...

Info

Dynamical Simulation of Folding Equilibria under Different Thermodynamic and Kinetic Conditions Until nine years ago, computer simulation could only be used to investigate the stability of the folds of proteins or peptides by submitting them in their folded form to strongly denaturing forces, e.g. at non-physiologically high temperatures 9, 10 . Folding into the native structure starting from an arbitrary structure under physiological conditions had not been observed at that time. In 1998 Daura...

Helical Structures Formed upon Adsorption

Tween Detergent

Adsorption of unfolded structures at interfaces can also induce the formation of helical conformations. Hydrophobins are among the best biosurfactants and Fig. 13.9 Self-assembly and conformational equilibria of hydrophobin SC3 in different environments and at different interfaces (Tween detergent poly(ethylene glycol) sorbitan monolaurate with n 20) 22 . (Adapted from ref. 22 .) Fig. 13.9 Self-assembly and conformational equilibria of hydrophobin SC3 in different environments and at different...

Adsorbed Sheet Structures at Interfaces

Another important class of secondary structures is the sheet motif. b-Sheet structures are abundant peptide and protein secondary structures, and similar secondary sheet structures are also found in a variety of artificial backbones (see Chapter 4). In most sheet structures, the individual foldamer chains are stretched and intermolecular interactions between different strands lead to the formation of two-dimensional ribbons or sheets via dimerization and further aggregation. A few examples of...

Inversion of Macromolecular Helicity

Right Handed Helix

Another interesting and unique feature of dynamic helical polymers is the reversible helix inversion helix-helix PM transition between right- and left-handed helical conformations regulated by external stimuli, such as a change in temperature, solvent or by irradiation with light. Because the extremely high sensitivity of dynamic helices to a chiral environment arising from a high cooperativity, the formation of an excess of the preferred helical sense can be altered, resulting in the inversion...