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The solution structure of eglin c based on measurements of many NOEs and coupling constants and its comparison with X‐ray structures
Author(s) -
Hyberts Sven G.,
Goldberg Matthew S.,
Havel Timothy F.,
Wagner Gerhard
Publication year - 1992
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560010606
Subject(s) - homonuclear molecule , chemistry , heteronuclear molecule , coupling constant , vicinal , molecular physics , ramachandran plot , crystallography , physics , molecule , nuclear magnetic resonance , stereochemistry , nuclear magnetic resonance spectroscopy , protein structure , quantum mechanics , organic chemistry
A high‐precision solution structure of the elastase inhibitor eglin c was determined by NMR and distance geometry calculations. A large set of 947 nuclear Overhauser (NOE) distance constraints was identified, 417 of which were quantified from two‐dimensional NOE spectra at short mixing times. In addition, a large number of homonuclear 1 H‐ 1 H and heteronuclear 1 H‐ 15 N vicinal coupling constants were used, and constraints on 42 χ 1 and 38 ϕ angles were obtained. Structure calculations were carried out using the distance geometry program DG‐II. These calculations had a high convergence rate, in that 66 out of 75 calculations converged with maximum residual NOE violations ranging from 0.17 Å to 0.47 Å. The spread of the structures was characterized with average root mean square deviations () between the structures and a mean structure. To calculate the unbiased toward any single structure, a new procedure was used for structure alignment. A canonical structure was calculated from the mean distances, and all structures were aligned relative to that. Furthermore, an angular order parameter S was defined and used to characterize the spread of structures in torsion angle space. To obtain an accurate estimate of the precision of the structure, the number of calculations was increased until the and the angular order parameters stabilized. This was achieved after approximately 40 calculations. The structure consists of a well‐defined core whose backbone deviates from the canonical structure ca. 0.4 Å, a disordered N‐terminal heptapeptide whose backbone deviates by 0.8–12 Å, and a proteinase‐binding loop whose backbone deviates up to 3.0 Å. Analysis of the angular order parameters and inspection of the structures indicates that a hinge‐bending motion of the binding loop may occur in solution. Secondary structures were analyzed by comparison of dihedral angle patterns. The high precision of the structure allows one to identify subtle differences with four crystal structures of eglin c determined in complexes with proteinases.