Conformational changes from

Conformational Changes from IVlolecular Dynamics Simulations... 

One interesting phenomenon was the effect of the boron substituent on enantioselectivity. The stereochemistry of the reaction of a-substituted a,/ -unsatu-rated aldehydes was completely independent of the steric features of the boron substituents, probably because of a preference for the s-trans conformation in the transition state in all cases. On the other hand, the stereochemistry of the reaction of cyclopentadiene with a-unsubstituted a,/ -unsaturated aldehydes was dramatically reversed on altering the structure of the boron substituents, because the stable conformation changed from s-cis to s-trans, resulting in production of the opposite enantiomer. It should be noted that selective cycloadditions of a-unsubsti-tuted a,/ -unsaturated aldehydes are rarer than those of a-substituted a,/ -unsatu-... 

The most likely way for pardaxin molecules to insert across the membrane in an antiparallel manner is for them to form antiparallel aggregates on the membrane surface that then insert across the membrane. We developed a "raft"model (data not shown) that is similar to the channel model except that adjacent dimers are related to each other by a linear translation instead of a 60 rotation about a channel axis. All of the large hydrophobic side chains of the C-helices are on one side of the "raft" and all hydrophilic side chains are on the other side. We postulate that these "rafts" displace the lipid molecules on one side of the bilayer. When two or more "rafts" meet they can insert across the membrane to form a channel in a way that never exposes the hydrophilic side chains to the lipid alkyl chains. The conformational change from the "raft" to the channel structure primarily involves a pivoting motion about the "ridge" of side chains formed by Thr-17, Ala-21, Ala-25, and Ser-29. These small side chains present few steric barriers for the postulated conformational change. 

The conformational changes which have been described so far are probably all relatively small local changes in the structure of H,K-ATPase. This has been confirmed by Mitchell et al. [101] who demonstrated by Fourier transform infrared spectroscopy that a gross change in the protein secondary structure does not occur upon a conformational change from Ei to 3. Circular dichroism measurements, however [102,103], indicated an increase in a-helical structure upon addition of ATP to H,K-ATPase in the presence of Mg and... 

Random coil conformations can range from the spherical contracted state to the fully extended cylindrical or rod-like form. The conformation adopted depends on the charge on the polyion and the effect of the counterions. When the charge is low the conformation is that of a contracted random coil. As the charge increases the chains extend under the influence of mutually repulsive forces to a rod-like form (Jacobsen, 1962). Thus, as a weak polyelectrolyte acid is neutralized, its conformation changes from that of a compact random coil to an extended chain. For example poly(acrylic acid), degree of polymerization 1000, adopts a spherical form with a radius of 20 nm at low pH. As neutralization proceeds the polyion first extends spherically and then becomes rod-like with a maximum extension of 250 nm (Oosawa, 1971). These pH-dependent conformational changes are important to the chemistry of polyelectrolyte cements. 

Xanthan is reported to undergo a chiroptically detected temperature or salt-driven conformational change from an ordered conformation at high salt and low temperature to a disordered conformation either associated with lowering the salt concentration, or with increasing the temperature (2-5). The primary structure of xanthan has been known for about a decade (6,7), but different structures have been suggested both for the ordered and disordered conformation. Some workers (8-13) conclude that the ordered conformation is double-stranded or double-helix, whereas others (14-17) claim that a single stranded description can account for the observed data under... 

There is now strong cumulative evidence that in the Ure2p, Sup35p, and HET-s systems, filamentation is based on polymerization of the prion domains into amyloid filaments. In this process, the prion domains undergo a conformational change from a natively unfolded state in which they are sensitive to proteolysis to a compact folded state rich in -structure in which... 

A. Fomili, B. Giabbai, G. Garau, and M. Degano, Energy landscapes associated with macromolecular conformational changes from endpoint structures, J. Am. Chem. Soc., 132 (2010) 17570-17577. 

Figure 11.13 Schematic representation of dynamic conformational change from diskhke to spherical morphologies in dendrimers.

Fig. 18 Schematic of the conformational changes from mushroom to brush state that occur in graft-polymerized PDMAm during the chain propagation process...

The comparative study of the n.m.r. spectra of L-rhamnose nucleosides 40a, 40b, and 44 and their 4 -keto derivatives 41a, 41b, and 45 revealed that the conformation changes from 4Ci to C4 on introduction of the carbonyl group.30... 

Polypeptides undergo a conformational change from helix to random coil when the solvent composition, pH or temperature is varied. Adsorption of polypeptides such as poly(/3-benzyl-L-glutamate), poly-proline, and polyhydroxyproline on glass was studied... 

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