8 research outputs found
Microsecond Time-Scale Conformational Exchange in Proteins: Using Long Molecular Dynamics Trajectory To Simulate NMR Relaxation Dispersion Data
With the advent of ultra-long MD simulations it becomes
possible
to model microsecond time-scale protein dynamics and, in particular,
the exchange broadening effects (<i>R</i><sup>ex</sup>)
as probed by NMR relaxation dispersion measurements. This new approach
allows one to identify the exchanging species, including the elusive
“excited states”. It further helps to map out the exchange
network, which is potentially far more complex than the commonly assumed
2- or 3-site schemes. Under fast exchange conditions, this method
can be useful for separating the populations of exchanging species
from their respective chemical shift differences, thus paving the
way for structural analyses. In this study, recent millisecond-long
MD trajectory of protein BPTI (Shaw et al. <i>Science</i> <b>2010</b>, <i>330</i>, 341) is employed to simulate
the time variation of amide <sup>15</sup>N chemical shifts. The results
are used to predict the exchange broadening of <sup>15</sup>N lines
and, more generally, the outcome of the relaxation dispersion measurements
using Carr–Purcell–Meiboom–Gill sequence. The
simulated <i>R</i><sup>ex</sup> effect stems from the fast
(∼10–100 μs) isomerization of the C14–C38
disulfide bond, in agreement with the prior experimental findings
(Grey et al. <i>J. Am. Chem. Soc.</i> <b>2003</b>, <i>125</i>, 14324)
Coordination to Imidazole Ring Switches on Phosphorescence of Platinum Cyclometalated Complexes: The Route to Selective Labeling of Peptides and Proteins via Histidine Residues
In this study, we have shown that
substitution of chloride ligand
for imidazole (Im) ring in the cyclometalated platinum complex Pt(phpy)(PPh<sub>3</sub>)Cl (<b>1</b>; phpy, 2-phenylpyridine; PPh<sub>3</sub>, triphenylphosphine), which is nonemissive in solution, switches
on phosphorescence of the resulting compound. Crystallographic and
nuclear magnetic resonance (NMR) spectroscopic studies of the substitution
product showed that the luminescence ignition is a result of Im coordination
to give the [Pt(phpy)(Im)(PPh<sub>3</sub>)]Cl complex. The other imidazole-containing
biomolecules, such as histidine and histidine-containing peptides
and proteins, also trigger luminescence of the substitution products.
The complex <b>1</b> proved to be highly selective toward the
imidazole ring coordination that allows site-specific labeling of
peptides and proteins with <b>1</b> using the route, which is
orthogonal to the common bioconjugation schemes via lysine, aspartic
and glutamic acids, or cysteine and does not require any preliminary
modification of a biomolecule. The utility of this approach was demonstrated
on (i) site-specific modification of the ubiquitin, a small protein
that contains only one His residue in its sequence, and (ii) preparation
of nonaggregated HSA-based Pt phosphorescent probe. The latter particles
easily internalize into the live HeLa cells and display a high potential
for live-cell phosphorescence lifetime imaging (PLIM) as well as for
advanced correlation PLIM and FLIM experiments