The paper describes how multiple crystal forms from a single drop were resolved by studying the conditions under which the crystals of each type grew using line search and response surface methods. In the end, crystals of cytidine deaminase were shown to grow optimally under at least two different conditions that different significantly in the concentration of water. Crystals from the dry form are discussed extensively in the literature; that of the wet form is described only in this paper. There are 7 extra molecules bound to a dimer interface cavity, leading to a modest conformational change in which the dimer assumes an asymmetric configuration. It appeared as well that there were different active site configurations in the two monomers.

This line of research preoccupied me at some length, and unpublished studies of the dependence of log(cat) vs log[H2O] was linear, with a slope of 7, matching the number of extra water molecules found in the altered dimer interface. Disagreement with Richard Wolfenden over the interpretation of this result, together with the fact that the resolution to which the crystals in the wet form diffracted prevented us from actually seeing confidently the nature of the ligands bound to the two active sites kept this work unpublished, unfortunately.

On Oct 28, 2016, at 8:47 AM, Phoebe A. Rice <[log in to unmask]> wrote:

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 [[log in to unmask]] on behalf of Roger Rowlett [[log in to unmask]]
Sent: Friday, October 28, 2016 9:36 AM
To: [log in to unmask]
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
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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