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Characterizing flexible and intrinsically unstructured biological macromolecules by SAS using the Porod‐Debye law
Author(s) -
Rambo Robert P.,
Tainer John A.
Publication year - 2011
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.21638
Subject(s) - small angle x ray scattering , flexibility (engineering) , debye , macromolecule , scattering , debye length , biopolymer , chemistry , mesoscopic physics , small angle scattering , statistical physics , biological system , chemical physics , physics , optics , polymer , condensed matter physics , statistics , mathematics , biology , biochemistry , organic chemistry , ion
Unstructured proteins, RNA or DNA components provide functionally important flexibility that is key to many macromolecular assemblies throughout cell biology. As objective, quantitative experimental measures of flexibility and disorder in solution are limited, small angle scattering (SAS), and in particular small angle X‐ray scattering (SAXS), provides a critical technology to assess macromolecular flexibility as well as shape and assembly. Here, we consider the Porod‐Debye law as a powerful tool for detecting biopolymer flexibility in SAS experiments. We show that the Porod‐Debye region fundamentally describes the nature of the scattering intensity decay by capturing the information needed for distinguishing between folded and flexible particles. Particularly for comparative SAS experiments, application of the law, as described here, can distinguish between discrete conformational changes and localized flexibility relevant to molecular recognition and interaction networks. This approach aids insightful analyses of fully and partly flexible macromolecules that is more robust and conclusive than traditional Kratky analyses. Furthermore, we demonstrate for prototypic SAXS data that the ability to calculate particle density by the Porod‐Debye criteria, as shown here, provides an objective quality assurance parameter that may prove of general use for SAXS modeling and validation. © 2011 Wiley Periodicals, Inc. Biopolymers 95: 559–571, 2011.