**************** The 7th., Lab Seminar *****************

Date: Mon, July 12, 2004  PM 1:30-

Place: No.616 Seminar room
　　　　　　 Graduate School of Information Science

Speaker: Yoichi Jindo

Title: Determination of the Three-Dimensional Structure of Crystalline
Leu-Enkephalin Dihydrate Based on Six Sets of Accurately Determined
Interatomic Distances from 13C-REDOR NMR and the Conformation-Dependent 13C
Chemical Shifts
J. Phys. Chem. B 1998, 102, 7476-7483
　　　　
Abstract:
 We have determined the three-dimensional structure of [13C,15N]-labeled
Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu)dihydrate (crystallized from aqueous
methanol) on the basis of six sets of accurately determined 13C･･･15N
interatomic distances by rotational echo double resonance (REDOR) and some
additional constraints from 13C chemical shifts. This compound has not yet
been refined by X-ray diffraction. Six kinds of[13C,15N]-doubly-labeled
samples, in which the doubly-labeled positions are four-bonds apart (four
samples) and five-bonds apart(two samples), were chemically synthesized.
These labeled peptides (100%) and an isotopically diluted one with unlabeled
samples (60% or 30%) were crystallized from aqueous methanol solution. 13C
or 15N chemical shifts were carefully evaluated prior to and after every
REDOR experiment in order to check that the crystalline polymorphs under
consideration were not modified either by loss of or by freezing of motion
of solvent molecules in the crystals. Accurate and precise interatomic
distances (±0.10 angstrom) were obtained from REDOR factors of infinite dilution,
which were extrapolated from the data of 100% and 30% isotopically diluted
samples to eliminate dipolar contributions from the labeled nuclei of
neighboring molecules in the crystals. These distance data were converted to
a possible set of local torsion angles (phi_i and psi_i)in a peptide unit of the
respective amino acid residue of interest using standard bond lengths and
angles in a sequential manner. It turned out that a unique set of the
torsion angles corresponding to the most appropriate three-dimensional
structure was determined with reference to some additional constraints from
the conformation-dependent displacements of 13C chemical shifts of certain
peptide units. The three-dimensional structure thus obtained was finally
subject to a calculation for energy minimization in order to ensure that the
conformation obtained was at least at one of local minima. Finally, the
biological consequence of the peptide structure thus determined is
discussed.
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