Kd. Rector et al., MUTANT AND WILD-TYPE MYOGLOBIN-CO PROTEIN DYNAMICS - VIBRATIONAL ECHOEXPERIMENTS, JOURNAL OF PHYSICAL CHEMISTRY B, 101(8), 1997, pp. 1468-1475
Picosecond infrared vibrational echo experiments on a mutant protein,
H64V myoglobin-CO, are described and compared to experiments on wild-t
ype myoglobin-CO. H64V is myoglobin with the distal histidine replaced
by a valine. The vibrational dephasing experiments examine the influe
nce of protein dynamics on the CO ligand, which is bound to the active
site of the mutant protein, from low temperature to physiologically r
elevant temperatures. The experiments were performed with a mid-infrar
ed free electron laser tuned to the CO stretch mode at 1969 cm(-1). Th
e vibrational echo results are combined with infrared pump-probe measu
rements of the CO vibrational lifetime to yield the homogeneous pure d
ephasing. The homogeneous pure dephasing is the Fourier transform of t
he homogeneous line width with the lifetime contribution removed. The
measurements were made from 60 to 300 K and show that the CO vibration
al spectrum is inhomogeneously broadened at all temperatures studied.
The mutant protein's CO vibrational pure dephasing rate is similar to
20% slower (narrower homogeneous pure dephasing line width) than the w
ild-type protein at all temperatures, although the only difference bet
ween the two proteins is the replacement of the wild-type's polar dist
al histidine amino acid by a nonpolar valine. These results provide in
sights into the mechanisms of the transmission of protein fluctuations
to the CO ligand bound at the active site, and they are consistent wi
th previously proposed mechanisms of protein-ligand coupling.