The use of resolution as sole criterion for validity of observations is not advisable. Interactions are inferred from the coordinates of interacting residues which are determined by examination of local electron density features. If you cannot assign rotamers etc. based on your electron density, then you are 'modeling' the interactions - you might still be able to say that certain residues are in proximity of other residues (and therefore are likely to matter for oligomerization), but you won't be able to say which particular features (hydrophobic, h-bond etc.) play a role in oligomer formation... In good cases (e.g. high NCS, well-ordered regions) you may be able to properly assign interactions even at 4A or worse. On the other hand if you have serious disorder, or other issues. then you may not be able to assign anything meaningful to pieces of structure even at 3A or better. In tight complexes, inter-subunit interactions are typiclly as 'good' as those in core regions of proteins. Therefore if you can unambiguously assign local features (e.g. conformations and so on) of protein core for parts of the oligomer, you should be able to assign tight interactions as well - with the above caveats, nevertheless. Loose, or fortuitous interactions (e.g. those that are very weak - like crystal contacts) should still be generally more ordered than corresponding residue types on the protein surface (i.e. not in contact) - however, given that subunits of complexes can be dramatically variable with respect to their order, it can be also the opposite - interaction regions are poorly defined as compared to the rest of a particular monomer.
Again, the use of resolution as some sort of rule of thumb in these matters is way inferior to manual examination of local density, computation of density-fit functions, and other techniques used to establish local structure quality. Artem Artem - Cosmic Cats approve of this message On Sun, May 24, 2015 at 4:54 AM, Smith Liu <[email protected]> wrote: > Dear All, > > In order to acceptably explain the salt bridges, hydrophobic interactions > and H-bonds among subunits in the crystal structure of a protein complex, > is there a threshold resolution of the crystal, for example, if the crystal > is poorer than 4A or 5A, the crystal structure solved cannot be used to > acceptably explain the intersubunit interactions at the non-covalen bond > level? > > Smith > > > > >
