Multiple Guinier regimes in a single curve

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Joined: 2021.05.07 21:37

Multiple Guinier regimes in a single curve

#1 Post by Murray » 2021.05.31 18:27


I have a question regarding the analysis of a SANS measurement from a contrast variation experiment. SANS was measured (please see attached screenshot) on a dodecameric (12 subunit, ~800 kDa, Dmax of ~300 angstroms, very flexible) enzyme reconstituted from partially deuterated beta (DSiR41) and protonated alpha subunits. Measurements were taken at the contrast-match point of the protonated components (41% D2O) so only DSiR41 was "visible" in the scattering.

Is it possible to obtain different Rg values from multiple Guinier regimes so long as one satisfies QRg < 1.3 limits? For example, DSiR41 satisfies these limits at multiple Q ranges: "low Q" (Q range between 0.004 - 0.01), "mid Q" (0.01-0.02), and "high Q" (0.02-0.07), yielding Rg values of ~100, ~60, ~20 angstroms each. This last Rg value makes sense in that the monomeric beta subunit has an Rg of ~20. One possibility is that the beta subunits are being repositioned from their isolated positions at the periphery of the complex to positions much closer, possibly interacting, and yielding the observed larger Rg values.

We re-measured DSiR41 at slightly higher concentration (v1 and v2 in the attached screenshot of DSiR41) and had similar results. The same protein stock was used to prepare multiple measurements, this sample seeing less % D2O than the others. This makes me think it unlikely that this phenomena is due to aggregation.

Perhaps I am misguided and/or there is a better approach in analyzing this sort of data. Any insights would be greatly appreciated. Thanks!

Screen Shot 2021-05-31 at 11.54.48 AM.png
Screen Shot 2021-05-31 at 11.54.48 AM.png (174.97 KiB) Viewed 2960 times

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