Globular proteins internal motions

Unlike for globular proteins, internal motions of IDPs can hardly be interpreted within the framework of the Lipari-Szabo model-free formalism. IDPs are dominated by segmental motions with low or negligible cooperativity between... 

Direct experiment-simulation quasielastic neutron scattering comparisons have been perfonned for a variety of small molecule and polymeric systems, as described in detail in Refs. 4 and 18-21. The combination of simulation and neutron scattering in the analysis of internal motions in globular proteins was reviewed in 1991 [3] and 1997 [4]. 

Table 1. Classification of internal motions of globular proteins...

Basic quantities and properties utilized for the characterization of macromolecules and colloidal particles are molecular mass (Al), molecular interactions (Aj), size (radius of g3uation Rg hydrodynamic radius Rh), particle scattering function (P(q)) defined by particle shape, and internal motions. Polydispersity can also be characterized by DLS. Combinations of these quantities are useful parameters to characterize maaomolecules or colloidal particles. There are a variety of monomolecular and multimolecular colloidal particles (e.g., globular proteins) flexible chain macromolecules, rigid and semifiexible rod-like macromolecules, micelles, and other self-assembled particles. We can choose suitable and efficient pathways to characterize them depending on their nature. LLS is a very powerful tool in this respect. 

The model-free approach is not applicable for non-globular, highly asymmetric, and partially folded or fuUy unfolded proteins as they do not meet the criteria of separation of internal and overall motions. The reconstruction of spectral density components, J(cOj), from Ri, R2, and N- H NOE measurements is possible but more experiments are required (e.g., relaxation measurements at several Bo values). Nevertheless, lUPs can also be analyzed in terms of raw data as done recently, e.g., for the unstructured protease inhibitor calpastatin (Kiss et al. 2008). 

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