Conformational state switch

The subunits can switch between two distinct conformational states, R and T, which are in equilibrium. 

Coiled Coils Designed to Switch Conformational State (2002 and 2003)... 

Fig. 3. Details of the seven-stranded /1-sheet and associated structures (A and B) in the post-rigor conformation and (C and D) in the pre-powerstroke conformation. The orientation of A and C is at right angles to that shown in Fig. 2. When attached to actin, it corresponds to that shown in Fig. 5B. The colors are as in Fig. 2. The views shown in B and D are at right angles to A and C looking out radially from the axis of the actin helix. Note the kink in the relay helix shown in C and D that leads to a 60° rotation of the converter domain. This in turn rotates the lever arm 60°. The P-loop (which constitutes the ATP-binding site) and the adjoining a-helix are shown in yellow. The flanking switch sequences (1 and 2) are also shown. The strands of the /1-sheet are numbered from the N-terminal (distal) end of the sheet. The lower part of strand 5 (light blue) constitutes switch 2. In the post-rigor state, switch 2 lies out of the plane of the /1-sheet (open) and in the pre-powerstroke state switch 2 is in the plane of the /1-sheet (closed).

Switching between different aggregated states resulting from a switching between different conformational states of the monomer units. 

The concept of cis-trans (Z-E) isomerism, originally used for the description of the relative geometry of olefins, has been extended to many other functions which feature a double bond character (pseudo double bonds), such as amides, as well as single bonds with a partial or complete limited rotation due to steric or stereoelec-tronic effects. Cis-trans isomerization (CTI) therefore exists in non-re-bonded or overcrowded molecules that switch from a given stable conformational state to another. This is the case of biaryl compounds which have been utilized in organic chemistry as the basis of molecular switches and rotors [1,2]. Nature has also exploited CTI of single bonds to increasing molecular diversity, in particular with the bulky thyroxin, a thyroid hormone, and the well-known disulfide bond which plays a critical role in the structure of peptides and in the conformation of proteins. 

Section 2.2.1.1 highlighted how the vibrational fine structure of pyrene, when dispersed under relatively dilute conditions, in the absence of excimer formation, can be used to reveal the pH-dependent response of PMAA. An alternative approach has used the occurrence of intermolecular excimer formation between dispersed pyrenyl probes under relatively concentrated conditions to monitor the conformational switch of the polymer [6,71]. When dispersed in PMAA, at concentrations higher than its solubility limit in water, partitioning of the probe between the hydrophobic polymer coil and the aqueous phase results [6,71]. Dependent on the pH of the solution and consequently the conformational state of the polyelectrolyte, the balance between these two distinct populations can be affected. For example, Fig. 2.7 shows the fluorescence emission spectra for the probe l,3-bis(l-pyrenyl)propane (1,3PP) when dispersed in aqueous solutions of PMAA [71]. At low pH, an emission spectrum consistent with that of monomeric unassociated pyrene is observed centered around... 

As already described in detail in the previous chapters, ion channels are proteins that consist of a few thousand amino acid residues and a few hundred carbohydrate residues that span the lipid cell membrane (I, 2). These channel proteins can have several different three-dimensional structures called conformational states. Some conformational states have a central hole, so that the channel is open to the flow of ions into or out of the cell. Other conformational states are closed to the flow of ions. Because these conformational states differ by energies that are less than the thermal fluctuations, a channel is always spontaneously switching between different open and closed states. 

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