Bert and Pascal are correct in that most alkyl glycoside detergent are notoriously difficult to crystallize in aqueous solution when you have the beta-anomer (what we normally buy). However, the alpha-anomers can be quite easy to crystallize and can contaminate batches of beta-alkyl glycoside detergents. While the quality control procedures are usually good enough to ensure that the alpha-anomer contamination of DDM, DM, and OG are low, it may not be low enough for all crystallization experiments. Twenty or so years ago, I was even shown a batch of "pure" beta-OG from a company I shall not name which was insoluble in water.

Some people have complained about this, but the impact of alpha-anomer contamination on crystal growth and spurious detergent crystallization is unknown. If this persists and you are sure that those are detergent crystals, you might ask to see information about alpha-anomer contamination for your batch of detergent. Companies like Anatrace will be quite forthcoming with information, but larger companies (Sigma or Rohm & Haas) may give you the run around.

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R. Michael Garavito, Ph.D.

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On Aug 4, 2009, at 12:51 PM, Van Den Berg, Bert wrote:

Hi Jose,

how do you know that those crystals were detergent and not protein? My impression is that it is really hard to crystallize DDM, and even harder for DM (solubilities > 20% in water). The easiest (?) way to check this may be to take some crystals, wash them well and run them out on a PAGE gel. If you don't see anything and you've taken enough crystals, then you're probably dealing with pure detergent crystals. As for your second point, you're right. For most low-cmc detergents the total detergent concentration will be substantially higher than reported, since a substantial amount is always bound to your protein. For 1 mM DDM, you would have only ~ 20 uM micelles, assuming an aggregation # of 50 (its higher). I don't think people measure the total detergent concentration in the end; for maltosides one could in principle do a Fehling's based assay to get the concentration.

Cheers, Bert

Bert van den Berg
University of Massachusetts Medical School
Program in Molecular Medicine
Biotech II, 373 Plantation Street, Suite 115
Worcester MA 01605
Phone: 508 856 1201 (office); 508 856 1211 (lab)
e-mail: [log in to unmask]
http://www.umassmed.edu/pmm/faculty/vandenberg.cfm

"Parveen Goyal" wrote:
> Hi All,
>
> I got some hexagonal crystals in one of my crystal condition. The protein is
> a membrane protein and contains 0.05% DDM. Has anybody seen DDM crysals
> and > if yes, how do they look like?
>
> thanks in advance
>
> Parveen Goyal
>