Dear Vincent, The resolution limit of reflections is a consequence of the closest distances in the structure that are consistent repeating units in the crystal lattice. This is not automatically linked to any particular features of a structure per se. In addition, while some of the structural fine features may be ordered at a particular resolution, other of those same features (e.g., different helices in a protein) may be disordered, depending on the properties of the particular protein and its crystal packing in a particular crystal form. What you can say is what level of structural detail is generally visible at a particular resolution, as a "rule of thumb", but even here, something can be visible and still open to interpretation when building the structure into the electron density.
In my experience, at about 5 A, you can start to make out individual alpha helices (appearing as cylinders) and beta sheets. At around 4 A, you can approximately assign some of the more bulky side chains if they are ordered (which they might not be). At 3 A, you can see a lot more side chain detail (and I've published structures at this resolution), but you have to be very careful in assignments to avoid errors. At 2 A, details tend to be a lot clearer. If your resolution is under 1 A, you begin to see details about the electron clouds around an atom that sometimes can be useful in supporting mechanistic conclusions. All this does not allow you to make a general statement about what type of structural element is always ordered. I hope this helps. -Daniel ________ Daniel M. Himmel, Ph. D. On Tue, Nov 28, 2017 at 9:44 AM, vincent Chaptal <vincent.chap...@ibcp.fr> wrote: > Hi, > > I've been searching but can't find what I am looking for so I thought I > ask specialists. > > I am curious about the link between resolution limits of reflections on > the detector, and what features are ordered in real space. > I saw the great movie by James Holton on resolution and features in the > electron density map, but I am looking for something more general. > I am thinking that a reflection on the detector originates from something > ordered within the crystal. The level of order would be different at > different resolution. > > If you can help me fill the void in this phrase: > I see spots at __A resolution, therefore I know that _____ features are > ordered in my crystal. > > intuitively, I would build the following scale: > 20A : the envelope is ordered > 10A: a finer envelope is ordered > 6A: alpha helices are ordered > 4-5A: beta sheets are ordered and some residues > 3-4A: residues start to be ordered > >3A: more and more order. > > Has this been described somewhere? I would appreciate any comments and > reevaluation of this scale. > > Thank you in advance. > All the best > Vincent > > > -- > > Vincent Chaptal, PhD > > Institut de Biologie et Chimie des Protéines > > Drug Resistance and Membrane Proteins Laboratory > > 7 passage du Vercors > <https://maps.google.com/?q=7+passage+du+Vercors%C2%A0%0D+69007+LYON%0D+FRANCE&entry=gmail&source=g> > > <https://maps.google.com/?q=7+passage+du+Vercors%C2%A0%0D+69007+LYON%0D+FRANCE&entry=gmail&source=g> > > 69007 LYON > <https://maps.google.com/?q=7+passage+du+Vercors%C2%A0%0D+69007+LYON%0D+FRANCE&entry=gmail&source=g> > > FRANCE > <https://maps.google.com/?q=7+passage+du+Vercors%C2%A0%0D+69007+LYON%0D+FRANCE&entry=gmail&source=g> > > +33 4 37 65 29 01 <+33%204%2037%2065%2029%2001> > > http://www.ibcp.fr > > >
