Dear All, Something like what Felix wrote is seen in the crystal structure of recombinant human acetylcholinesterase (rhAChE) (PDB-ID: 3lii), with two molecules are seen in the asymmetric unit. * In one molecule, the active-site gorge (where inhibitors normally lie) is occupied with part of a peptide loop from a symmetrically related rhAChE. * While the corresponding region of the other copy of rhAChE is void of this peptide. See figs 15-16 in: Dvir, H., Silman, I., Harel, M., Rosenberry, T. L. & Sussman, J. L. (2010). "Acetylcholinesterase: From 3D structure to function" Chemico-Biological Interactions 187, 10-22. * So, in essence, no reason to ever assume that two copies in asymmetric unit will be identical, or have identical inhibitors bound, or 'surrogate inhibitors' (like in this case) bound. Sometimes differences are due to difference in crystal packing Best regards, Joel
On 7 Jan 2013, at 11:58, Felix Frolow wrote: I apologise for typing blinbly: " if one is in, the second can't be" FF Dr Felix Frolow Professor of Structural Biology and Biotechnology, Department of Molecular Microbiology and Biotechnology Tel Aviv University 69978, Israel Acta Crystallographica F, co-editor e-mail: mbfro...@post.tau.ac.il<mailto:mbfro...@post.tau.ac.il> Tel: ++972-3640-8723 Fax: ++972-3640-9407 Cellular: 0547 459 608 On Jan 7, 2013, at 11:48 , Felix Frolow <mbfro...@post.tau.ac.il<mailto:mbfro...@post.tau.ac.il>> wrote: Why not? They can be mutually excluding! If one is in, the second can be. This phenomenon brakes a local symmetry. FF Dr Felix Frolow Professor of Structural Biology and Biotechnology, Department of Molecular Microbiology and Biotechnology Tel Aviv University 69978, Israel Acta Crystallographica F, co-editor e-mail: mbfro...@post.tau.ac.il<mailto:mbfro...@post.tau.ac.il> Tel: ++972-3640-8723 Fax: ++972-3640-9407 Cellular: 0547 459 608 On Jan 7, 2013, at 11:28 , Xiaopeng Hu <huxp...@mail.sysu.edu.cn<mailto:huxp...@mail.sysu.edu.cn>> wrote: Dear All, We recently resolved an enzyme/inhibitor complex structure. The enzyme contains two NCS related active site and we did find extra density in both of them.However we observed that the two inhbitor moleculors are not NCS related, but partly overlaped if make a NCS moleculor. Has anyone else observed this before? Thanks for any help and suggestion! Best, Xiaopeng Hu
