In two Nature articles, Kern and collaborators were able, in effect,
to create a motion picture of an enzyme as it actually changed shape,
or conformations, in the absence of the substrate. �It�s really a
paradigm shift,� said Kern. Earlier studies had been able only to
create snapshots of enzymes frozen in time, obscuring their true
restless, twitching selves.
The three-year study represents a breakthrough in scientific
understanding of the dynamic personalities of enzymes. For years, Kern
has dedicated herself to capturing how enzymes move and change shape
through time. She pioneered the use of nuclear magnetic resonance
(NMR), which can detect the motion of individual atoms in a protein,
in this biophysical application.
But in this study, Kern, who earlier in life was the point guard on
the East German national women�s basketball team, knew she had to
create a gold-standard strategy that would capture not only the motion
of a key protein, but its structures, as well. She had to make sure
that the fleeting, more infrequent shapes of enzymes couldn�t
essentially wiggle out of the picture. These rarer enzyme states are
critical to understand, as they are the ones most relevant to better
drug design.
Ultimately, Kern harnessed five different elegant techniques,
including X-ray crystallography, (NMR), single-molecule fluorescence
resonance energy transfer (FRET), computer simulations of molecular
dynamics, and paramagnetism, to reveal the full picture of how
proteins fold in those infrequent, yet lightening-fast intermediate
states between inactivity and activity. Each technique provided a
piece of the puzzle.
�The big goal here is to understand proteins well enough so that we
can actually predict how they will behave,� said Kern. These
short-lived structures are most likely to have a higher affinity to
drug molecules. Instead of relying on trial and error, scientists may
be able to rationally design drugs to specifically bind to these
intermediate conformations, according to Kern.
With the ability to capture an enzyme in real time as it is moving
toward the active state, Kern and co-workers were able to detect
picosecond (one millionth of one millionth of a second) changes, the
fast smaller conformational motions, as well as the millisecond
large-scale motions that are a result of the many fast motions.
�This work will lead to understanding the physical nature of proteins
not as a static picture but as an ensemble of structures,� said Kern.
The research was supported by the Howard Hughes Medical Institute,
National Institutes of Health, the Department of Energy, and the
American Heart Association.
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