Couldn't they simply be too thin? After all, unit cell dimensions are routinely about 0.01um, so if these needles are only fraction of a micron thick, there is simply not enough material for diffraction.
Nice looking but non-diffracting protein crystals are too disordered (i.e. while packing is present, there is no long-range spatial correlation among individual unit cells). On Mon, 2010-04-19 at 11:35 +0800, tat cheung cheng wrote: > Thank you. Forget to mention, no diffraction observed no matter with > or without cyro cooling. > > > > ______________________________________________________________________ > 寄件人﹕ "tom.p...@csiro.au" <tom.p...@csiro.au> > 收件人﹕ theif...@yahoo.com.hk > 傳送日期﹕ 2010/4/19 (一) 11:29:38 AM > 主題： RE: [ccp4bb] Re： [ccp4bb] Mysterious Crystals? > > Hello Tc, > > > > It isn’t that unusual to get protein crystals that don’t diffract. > This happens probably 50% of the time. One can try dehydration of the > crystals, crystal annealing and additive screens to see if any of > these things will give you some diffraction. In addition, you didn’t > mention whether you froze these crystals- one should also try putting > a crystal in the beam without cryo-cooling, as cryo-cooling can often > be detrimental to diffraction. > > > > Cheers, tom > > > > > ______________________________________________________________________ > From:CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of > tat cheung cheng > Sent: Monday, 19 April 2010 1:26 PM > To: CCP4BB@JISCMAIL.AC.UK > Subject: [ccp4bb] Re： [ccp4bb] Mysterious Crystals? > > > > > Yes, I have just done that. They are protein. But if they are protein, > why no diffraction? That's intriguing. > > > > > > ______________________________________________________________________ > 寄件人﹕ Jürgen Bosch <jubo...@jhsph.edu> > 收件人﹕ccp...@jiscmail.ac.uk > 傳送日期﹕ 2010/4/19 (一) 10:57:40 AM > 主題： Re: [ccp4bb] Mysterious Crystals? > > Fish and wash some crystals then run them on a SDS-gel, then you will > know for sure if it's protein or not. > > > > > J僡gen > > On Apr 18, 2010, at 10:46 PM, tat cheung cheng wrote: > > > > > Hi all, > > I have got some crystals, the purified protein was in Tris buffer with > 300mM NaCl for crystallization. they grew in light weight PEG, PEG400 > or monomethyl ethyl PEG500, they were needle shaped, could be long > (~0.2mm) but very thin all the time and sometimes grew into sea-urchin > like needle cluster. > What interesting is, when i gridded crystallization conditions against > pH or PEG amount, the crystals sizes and shapes varied, and the > crystals were fragile so i believed they were protein crystals in > nature. But upon X-ray diffraction, they gave no reflection at all, > not even a faint spot. > I wonder, beside silly mistakes like misalignment of the crystal to > the beam, not enough exposure time, what could be the reason for this > mysterious crystals? Are they protein or PEG or what? > Thanks very much. > > Tc > > > > > > > > > - > > > J僡gen Bosch > > > Johns Hopkins Bloomberg School of Public Health > Department of Biochemistry & Molecular Biology > Johns Hopkins Malaria Research Institute > 615 North Wolfe Street , W8708 > Baltimore , MD 21205 > Phone: +1-410-614-4742 > Lab: +1-410-614-4894 > Fax: +1-410-955-3655 > http://web.mac.com/bosch_lab/ > > > > > > > > > > > -- Edwin Pozharski, PhD, Assistant Professor University of Maryland, Baltimore ---------------------------------------------- When the Way is forgotten duty and justice appear; Then knowledge and wisdom are born along with hypocrisy. When harmonious relationships dissolve then respect and devotion arise; When a nation falls to chaos then loyalty and patriotism are born. ------------------------------ / Lao Tse /
