[3dem] Interpretation of strange objects in a cryo-EM sample

Thu Apr 13 07:05:05 PDT 2023

James,

Those images look consistent with large particles that exclude water.  I don’t know the expected sizes of micelles, however.  If the appearance changes with increased exposure to the electron beam, then I would agree that you have beam damage.  Be careful of claims of “pure” samples.  I often see much more than what is claimed to be in a pure sample.  Is what you are looking for supposed to be smaller than these particles?  As Vincent suggests, you may have constructs different from what you expect.  Your lower magnification picture suggests a diluted sample to me.

David

From: 3dem <3dem-bounces at ncmir.ucsd.edu> on behalf of vincent Chaptal <vincent.chaptal at ibcp.fr>
Date: Thursday, April 13, 2023 at 7:58 AM
To: "Kizziah, James" <kizziah4 at uab.edu>, "3dem at ncmir.ucsd.edu" <3dem at ncmir.ucsd.edu>
Subject: Re: [3dem] Interpretation of strange objects in a cryo-EM sample

Dear James,

you didn't say which detergent the micelles would be orinigating from, it changes from detergent to detergent.

But in any case, beside the mix DDM/CHS which forms small micelles when concentrated but large objects when diluted, most micelles are much much smaller, say 30-50Å or so.

I think there is an article by the group of Arne Moeller on detergent micelle observation by negative stain, I don't recall if they tried in cryo.

Best
Vincent
Le 13/04/2023 à 15:48, Kizziah, James a écrit :
Hi all,

We have imaged a cryo-EM sample presumed to contain micelles and observed the large, white objects full of/covered with junk shown in the attached images. Our best guess is that these are (or were) the micelles and have been destroyed by the electron beam, contact with the air water interface, or both, after vitrification. Has anyone seen something like this before or does anyone have alternative interpretations?

Glow-discharged lacey carbon grids plunge frozen with a Mark IV Vitrobot, clipped and imaged on a Glacios.

Thanks,
James

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