12/24/2022 0 Comments Usp resolution calculatorIn order to derive structural information of proteins in solution from SAXS curves, several software packages for data analyses and evaluations, such as ATSAS 1 and SCATTER, 2 are currently available. The angular‐averaging of 2D detector patterns yields a one‐dimensional (1D) scattering intensity as a function of the modulus of the scattering vector, I( q). In modern laboratory setups and synchrotron radiation‐based beamlines, SAXS data are recorded by two‐dimensional (2D) detectors. For a dilute set of proteins with random orientations, the scattering intensity defined in the reciprocal space is isotropic. The experimental SAXS intensity associated to a set of proteins of the same nature in dilute solution-after subtracting the parasitic scattering intensity produced by the buffer under the same experimental condition-is proportional to the scattering intensity produced by a single protein averaged over all possible orientations. The SAXS method allows for investigations of both, well‐structured and disordered macromolecules in solution, neither requiring crystallization procedures nor highly elaborate sample preparations. Small‐angle X‐ray scattering (SAXS) is an experimental technique frequently applied to low‐resolution structural studies of macromolecules embedded in a homogeneous liquid medium, over a molecular size scale within the 1–100 nm range. Our tests show discrepancies of approximately 21% for the proteins with molecular shape aspect ratios up to 18. In case of elongated molecules, discrepancy value can be significantly higher. These tests reveal that the use of SAXSMoW 2.0 allows for determinations of molecular weights of proteins in dilute solution with a median discrepancy of about 12% for globular proteins. The new program was extensively tested by applying it to many experimental SAXS curves downloaded from the open databases, corresponding to proteins with different shapes and molecular weights ranging from ~10 kDa up to about ~500 kDa and different shapes from globular to elongated. SAXSMoW 2.0 exhibits new features which allow for the direct input of experimental intensity curves and also automatic modes for quick determinations of the radius of gyration, volume, and molecular weight. The first version of this calculator has been widely used during the last decade and applied to analyze experimental SAXS data of many proteins and protein complexes. We describe here a program SAXSMoW 2.0 for robust and quick determination of molecular weight and oligomeric state of proteins in dilute solution, starting from a single experimental small‐angle scattering intensity curve, I( q), measured on a relative scale. Knowledge of molecular weight, oligomeric states, and quaternary arrangements of proteins in solution is fundamental for understanding their molecular functions and activities.
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