Primary protein response after ligand photodissociation in carbonmonoxy myoglobin

*Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Honmachi, Kawaguchi 332-0012, Japan;
^†School of Advanced Sciences, Graduate University for Advanced Studies, Hayama 240-0193, Japan;
^‡Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Okazaki 444-8787, Japan; and
^¶Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan

Edited by Robin M. Hochstrasser, University of Pennsylvania, Philadelphia, PA, and approved April 24, 2007 (received for review December 26, 2006)

Abstract

Time-resolved UV resonance Raman (UVRR) spectroscopic studies of WT and mutant myoglobin were performed to reveal the dynamics of protein motion after ligand dissociation. After dissociation of carbon monoxide (CO) from the heme, UVRR bands of Tyr showed a decrease in intensity with a time constant of 2 ps. The intensity decrease was followed by intensity recovery with a time constant of 8 ps. On the other hand, UVRR bands of Trp residues located in the A helix showed an intensity decrease that was completed within the instrument response time. The intensity decrease was followed by an intensity recovery with a time constant of ≈50 ps and lasted up to 1 ns. The time-resolved UVRR study of the myoglobin mutants demonstrated that the hydrophobicity of environments around Trp-14 decreased, whereas that around Trp-7 barely changed in the primary protein response. The present data indicate that displacement of the E helix toward the heme occurs within the instrument response time and that movement of the FG corner takes place with a time constant of 2 ps. The finding that the instantaneous motion of the E helix strongly suggests a mechanism in which protein structural changes are propagated from the heme to the A helix through the E helix motion.

Footnotes

^‖To whom correspondence should be addressed. E-mail: mztn{at}chem.sci.osaka-u.ac.jp
Author contributions: A.S., T.K., and Y.M. designed research; A.S. and Y.G. performed research; A.S. and Y.M. analyzed data; and A.S., T.K., and Y.M. wrote the paper.
↵ ^§Present address: Toyota Physical and Chemical Research Institute, Nagakute, Aichi 480-1192, Japan.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0611560104/DC1.
Abbreviations:

Hb,

hemoglobin;

Mb,

myoglobin;

deoxyMb,

deoxy form of Mb;

MbCO,

carbon monoxide-bound form of Mb;

UVRR,

ultraviolet resonance Raman.