Calculation of structural parameters from hydrodynamic data

Abstract

Biopolymers of simple overall shape (nonconjugated and conjugated proteins, viruses, ribonucleic acids) can be modeled by whole-body approaches, approximating their shape by prolate/ oblate ellipsoids of revolution or spheres. A sophisticated rearrangement of the theoretical formalism already applied for the prediction of hydrodynamic data from solution scattering or crystal data allows the inverse procedure, the prediction of structural parameters on the basis of hydrodynamic data. Sedimentation and diffusion coefficients, in addition to molar masses, partial specific volumes and values for hydration, are used to predict structural parameters typical of small-angle X-ray scattering studies (radii of gyration, volumes, surface-to-volume ratios and surface areas), together with estimates of axial ratios. For particles of simple shape such as globular proteins, fair agreement between observed and predicted values was achieved. Far-reaching conformity between experiments and calculations was also obtained for the prediction of subtle ligand-induced shape changes. A critical assessment of errors reveals the validity of anticipations of structural parameters from hydro-dynamic data. The accuracy to be obtained, however, turns out to be less than for the reverse procedure. Use of viscosity data for parameter predictions cannot be recommended.