Back in my grad school days, we had crystals (of gamma delta resolvase large fragment) like that: at high protein concentrations, we'd get P6422 with 1/asymmetric unit, and at lower concentrations, C2221 with 3/asymmetric unit (with an imperfect ncs 2fold 60 degrees from the xtal fold, and very similar overall packing) that diffracted better. Sometimes the latter would grow off the sides of the former. Phoebe ________________________________ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Roger Rowlett [rrowl...@colgate.edu] Sent: Friday, October 28, 2016 9:36 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Two SGs in one droplet?
I've seen this kind of thing before. Case 1: two crystal forms in the same droplet, C2 and C222. If you looked closely, you could tell them apart and I was pretty good at getting a high percentage of the desired space group by looking at the crystal forms. The C2 form diffracted better, so I fished for that one. Case 2: A mixture of crystals, C2 and C2 with the long axis doubled in length, caused by asymmetric ligand binding. In the "double-size" C2 crystal form, ligands bound to only 10 of the 12 chains in the double-size ASU, which no longer conformed to two adjacent "normal-size" C2 ASUs. In the "normal" size C2 form, all 6 protein chains in the ASU bound ligand. Cheers, _______________________________________ Roger S. Rowlett Gordon & Dorothy Kline Professor Department of Chemistry Colgate University 13 Oak Drive Hamilton, NY 13346 tel: (315)-228-7245 ofc: (315)-228-7395 fax: (315)-228-7935 email: rrowl...@colgate.edu<mailto:rrowl...@colgate.edu> On 10/28/2016 9:13 AM, Sam Tang wrote: Dear all Sorry for going a bit off-topic in this thread. May I seek your advice as on whether you have experienced that crystals being obtained from the same droplet, looking alike under microscope (rod shape) and in fact growing possibly from a same nuclei, give two space groups after indexing? I recently obtain crystals for a protein (co-crystallized with a nucleic acid ligand) and collected two datasets from synchrotron. Although these two crystals are from the same drop, the SG and unit cell dimensions are very different: Xtal1: C121 (156 60 105 90 111 90) (L-test, Pointless shows that there is no twinning), ~2.5 Angstrom Xtal2: P1 (53 60 79 106 105 98), ~3 Angstorm Would it be possible that the ligand changes the SG of the crystal so that only one of the forms contains the ligand? Any advice is appreciated and thanks a lot in advance for your input. Regards Sam Tang Biochemistry Programme, School of Life Sciences, CUHK
