Clamp domain

FIGURE 5-12 A processive clamp model for the ATPase cycle of the ABC transporter Mdllp. ATP binding (step I) on NBD domains of both monomers induces formation of the dimer (step 2). After ATP hydrolysis by the first NBD (step 3), either the P, is released first (step 4), followed by hydrolysis of the second ATP step 5) and release of the second P, step 8), or the second ATP is hydrolyzed first step 6) and then both phosphates are set free steps 7 and 8). After both ATPs are hydrolyzed to ADP and both phosphates are released, the dimeric complex dissociates step 9) and ADP step 10) is released. The hydrolysis cycle can then start again with ATP binding. (With permission from Fig. 7 of reference [34].)... 

In such a measurement, the sample is clamped as lightly as possible, and the displacement of the surface in monitored. The amount of sample clamping is important, because the mechanical constraints can impact the ferroelastic response of the sample. That is, in samples where the mechanical coercive stress is low, it is possible to change the domain state of the material by improperly clamping it in the sample fixture. This is especially important in elastically soft piezoelectrics, such as many of the relaxor ferroelectric PbTiC>3 single crystals. 

Other common means for determining the direct d33 coefficients of bulk samples include Berlincourtstyle approaches. Berlincourt meters are available commercially from several sources. In most cases, the sample to be measured is mechanically clamped between jaws with pressures on the order of a few N. The charge output due to a small mechanical oscillation (forces 0.1-0.3N) is then determined. It is important to note that this technique is appropriate for measurements of bulk samples with stable domain states, only. Measurement accuracy is also better when highly resistive samples are used. 

The (t2 protein is a clamp attached to the 2,1 shell. The protein has three distinct binding sites on the shell, one of which is across a 2-fold axis. There are thus 150 copies of this protein. The 417 residues form a globular domain consisting mostly of helices (Fig. 13 see Color Insert). Most of the structure is formed by a repeated motif of about 150 residues. The motif starts with a strand and is followed by three helices, the last two of which are antiparallel. A loop region containing a two-stranded... 

Chapman and Liljas, Fig. 13. Reovims proteins, (a) The X2 turretprotein (Reinisch 2000). The individual domains are marked, (b) The cr2 clamp protein (Reinisch etal, 2000). The two halves of the main part of the protein have approximate 2-fold symmetry. The view is dovm the symmetry axis, (c) The capsid protein (Olland et at, 2001). 

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