Analyzing flexible proteins using small angle X-ray scattering

Efstratios Mylonas
EMBL, Hamburg Outstation, Germany

The number of natively unfolded proteins or proteins with long flexible linkers that have been identified and studied during the recent years is persistently increasing. They are involved in various biologically significant functions such as transcriptional/translation regulation, cell cycle control, modulation of the assembly of other proteins, neuron development etc and are most common in higher organisms. Structural analysis of flexible macromolecular systems is a difficult task since high resolution techniques are barely applicable.

The lecture will concentrate on how to apply solution small angle X-ray scattering (SAXS) to answer structural questions for flexible systems, while discussing the concept of "structure" of such systems. Information from other methods such as NMR, EM or FRET can also be introduced in the modeling process as additional restraints. Two distinct approaches can be utilized to analyze the data. The simplest of the two is to produce a SAXS-constrained model which represents on average the shape of the particle in solution e.g. in order to elucidate the relative position of the domains of a multidomain protein. This can be done with existing software that is also used for folded proteins. Of course, such an approach ignores the intrinsic flexibility of the molecules. Using the recently developed Ensemble Optimization Method EOM it is possible to fit a SAXS curve to multiple models selected from a randomly generated pool. This approach can provide information about the conformational space a protein can explore.

Bernado, P., Mylonas, E., Petoukhov, M. et al. (2007) Structural Characterization of Flexible Proteins Using Small-Angle X-ray Scattering. Journal of the American Chemical Society, 129, 5656-5664

Date/time: Thursday, 23 October, 14:45