Paramagnetic Constraints for Structure Analysis

The conformational space sampled by the two-domain protein calmodulin has been explored by an approach based on four sets of NMR observables obtained on Tb and Tm -substituted proteins. The observables are the pseudocontact shifts and residual dipolar couplings of the C-terminal domain when lanthanide substitution is at the N-terminal domain. Each set of observables provides independent information on the conformations experienced by the molecule. It was found that not all sterically allowed conformations are equally populated. For example, taking the N-terminal domain as the reference, the C-terminal domain preferentially resides in a region of space inscribed in a wide elliptical cone. 

Determinations based on this approach include human a-parvalbumin by substitution of Dy in a Ca binding site the Rhodopseudomonas palustris cytochrome Csse oxidized cytochrome bs and MetgoAla cyano-cytochrome c. Banci et al have determined the solution structure of oxidized cytochrome Css3 from Bacillus pasteurii. 

Assfalg et have determined the solution structure of enriched yeast iso-l-ferricytochrome c which contained three mutations designed to produce a single conformer. The global structure of the protein was determined using NOE s, backbone angle constraints, and pseudocontact shifts as constraints. Yao et have determined the solution structure of cyanoferricytochrome c. 

Assfalg et al have determined the solution structure of fully oxidized mutant form of cytochrome c , which is paramagnetic with three paramagnetic centers. The assignment strategy and the algorithm of an automated program used in the analysis of H NMR spectra are described. 

Bertini et have studied the question of whether reliable models for a protein of unknown structure can be constructed from that of a protein of known structure if the sequence homology is greater than 30%. They modeled the structure of cytochrome c556 on that oT cyt c and validated the model using paramagnetic structure constraints (pseudocontact shifts and self-orientation residual dipolar couplings) without determining the full solution structure. 

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