Backbone Dynamics and Structural Characterization of the Partially Folded A State
of Ubiquitin by 1H, 13C, and 15N Nuclear Magnetic Resonance Spectroscopy†
posted on 1997-10-21, 00:00authored byBernhard Brutscher, Rafael Brüschweiler, Richard R. Ernst
Structure and dynamics of the partially folded A state of
ubiquitin in a 60%/40% methanol/water mixture at pH 2 was studied by two- and three-dimensional nuclear
magnetic resonance spectroscopy
(NMR) using fully 13C,15N-labeled ubiquitin.
Complete backbone 13CO,
13Cα, 15N, and
1HN assignment
was achieved. 13CO and
13Cα chemical shifts and
1H−1H nuclear Overhauser enhancement
(NOE)
connectivities indicate different behavior for the N-terminal and the
C-terminal halves of the protein. In
the N-terminal half of the A state, comprising the antiparallel
β-sheet and the central α-helix, the native
secondary structural elements are largely conserved. The
C-terminal half, which is in the native form
rich in β-strand character, undergoes a methanol-induced transition
to a dynamic state with a uniformly
high propensity for helical structure. This behavior is also
reflected in backbone 15N relaxation data,
indicating the presence of three loosely coupled secondary structural
segments with enhanced internal
mobility as compared to the native state.