Sample requirements

The sample concentrations must be determined as precise as possible (accuracy better than 10% is required). The concentrations are necessary to normalize the scattering data. Bradford assays are usually not sufficiently precise, OD measurements @280 nm are better. At the beamline, a Nanodrop spectrophotometer is available. As of November'2008, a refractometer is also installed, which allows one to measure the concentration for the proteins lacking aromatic residues.

A single SAXS measurement on X33 requires about 30-60 μl of sample, and the exposure time is about 2 minutes. The samples can be damaged by synchrotron radiation during the collection time. A reducing agent (e.g. 2mM DTT) is typically added to the sample before the experiment to diminish the damage/aggregation during the data collection.

Each measurement of the macromolecular solution requires two measurements of the corresponding buffer (before and after the sample). The buffers should not contain excessive amounts of additives (e.g. not more than 0.5M NaCl, not more than 5% glycerol, not more than 5 mM ATP etc) unless this is unavoidable. If you need to work with the buffers containing excessive amounts of additives, please consult us in advance.

The users must verify the sample monodispersity (desirably > 90%) prior to coming for the synchrotron radiation measurements e.g. by native gel filtration, ultracentrifugation, DLS etc. If the sample is aggregated, the scattering data will be difficult or even impossible to interpret. Please note that a single band on the SDS gel goes not indicate monodisperse solutions — a single band on the native gel is required!

Typically, for each sample a concentration series (e.g. 1, 2, 5, 10 mg/ml) has to be measured. If your proteins tend to (or may) aggregate at higher concentrations, it is highly recommended to bring the low concentration stocks and concentrate the samples prior to the synchrotron radiation measurements. If the sample is well behaved, one may bring high concentration stocks to dilute them before the measurements.

The cell is cleaned and refilled automatically after each measurement. You should bring sufficient amount (> 10 ml) of matching buffer(s) to dilute the samples if necessary and also to clean the cell.

If you do not bring your samples with you - be sure to send them well in advance. Even with courier service (FedEx, DHL, TNT, UPS, etc) allow a week for the samples to arrive. Send frozen samples only on Monday or Tuesday to ensure delivery before Saturday and put sufficient amount of dry ice. Note that the samples will be stored exactly according to your instructions upon arrival — write them clearly and label the samples.

Address the samples to:
Dr. Dmitri Svergun
EMBL c/o DESY
Notkestrasse 85, Geb. 25 A
22603 Hamburg
Germany