Angular constraints

Park SH, Das BB, De Angelis AA, Scrima M, Opella SJ (2010) Mechanically, magnetically, and rotationally aligned membrane proteins in phospholipid bilayers give equivalent angular constraints for NMR structure determination. J Phys Chem B 114 13995-14003... 

Crystal system (7) Characteristic symmetry Lattice [Laue) symmetry Axial and angular constraints from symmetry ... 

Here, the experimental error for each 0 value is introduced and shown as the width of the lines. The black area indicates the most accurate region which satisfies all of the observed bond orientations within experimental error. By addition of the angular constraint 0cr> to those obtained from and solid-state NMR, a further narrow (more... 

Fig. 8.7. Combination of four bond orientations (Anh. 6nc, Sco and 0cn) of Ala site of silk fiber within -180° < (f><0° and 0° < i/< < 180°. The width of each line means experimental error ( 5°). There are two lines indicated by arrows for each bond orientation. The black area (A-D) indicate the most accurate

In many cases, the sensitivity is improved by taking advantage of the Ca labeled sites in peptides and proteins with detection. The similarities between experimental and simulated spectra demonstrate the validity of the recoupling mechanism and identify the potential for applying these experiments to virus particles or membrane proteins in phospholipid bilayers however, further development is needed in order to derive quantitative distance and angular constraints from these measurements. ... 

Firstly, and most importantly, a substructure search requires that the user who is posing the query must already have acquired a well-deffned view of what sorts of structure are expected to be retrieved from the database. For example, a 3D substructure search requires sufficient information about the geometric requirements for activity to be able to specify distance and/or angular constraints to characterize those molecules, and just those molecules, that can fit some putative receptor site. This implies that some form of pharmacophore map has been created, using techniques such as those described by Bures et al., which in turn implies that it has already been possible to identify sufficient active substances to generate the map. Substructure search is much less appropriate at the start of an investigation when perhaps only one or two active structures have been identified and when it is not at all clear which particular feature(s) within them are responsible for the observed activity. 

Solution-derived RDCs are important angular constraints in the structure determination of membrane proteins as well as their solution state counterparts. Strained polyacrylamide gels are able to induce the necessary weak alignment of protein samples embedded in spherical micelles. The incorporation of proteins into the gel matrix is not straightforward, but Jones and Opella have outlined a number of methods for this. Similar methods were used by Howell et al. in their structure determination of the mercury transport... 

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