  The current paradigm for protein structure determination by NMR spectroscopy
has thus far been based on collecting distance restrains between pairs of
nuclei in the form of nuclear Overhauser enhancements (NOE). These, have in
some circumstances been supplemented with other information sources such as
paramagnetic relaxation enhancements or residual dipolar couplings. Here, we
report for the first time a protein structure determination by NMR without the
use of NOEs. The protein PioC from Rhodopseu-domonas palustris TIE-1 is an
HIPIP where the 4Fe4S cluster is paramagnetic and provides the source of
Paramagnetic Relaxation Enhancements (PRE) used as alternative distance
constraints. Comparison of the family of structures obtained by NOE structural
restraints, with that obtained by PRE and with the family of structures
obtained by combining NOEs and PREs reveals that the pairwise RMSD between them
are similar and comparable with the precision within each family. This work
sets the stage for the structural characterization of small and dynamic
paramagnetic metalloproteins opening a new paradigm in the use of NMR in
structural biology.
