TY - JOUR
T1 - Ligand migration in the truncated hemoglobin-II from Mycobacterium tuberculosis
T2 - The role of G8 tryptophan
AU - Guallar, Victor
AU - Lu, Changyuan
AU - Borrelli, Kenneth
AU - Egawa, Tsuyoshi
AU - Yeh, Syun Ru
PY - 2009/1/30
Y1 - 2009/1/30
N2 - Resonance Raman studies show that the heme-bound CO in trHbO, a truncated-II hemoglobin from Mycobacterium tuberculosis, is exposed to an environment with a positive electrostatic potential. The mutation of Trp(G8), an absolutely conserved residue in group II and III truncated hemoglobins, to Phe introduces two new Fe-CO conformers, both of which exhibit reduced electrostatic potentials. Computer simulations reveal that the structural perturbation is a result of the increased flexibility of the Tyr(CD1) and Leu(E11) side chains due to the reduction of the size of the G8 residue. Laser flash photolysis studies show that the G8 mutation induces 1) the presence of two new geminate recombination phases, one with a rate faster than the time resolution of our instrument and the other with a rate 13-fold slower than that of the wild type protein, and 2) the reduction of the total geminate recombination yield from 86 to 62% and the increase in the bimolecular recombination rate by a factor of 530. Computer simulations uncover that the photo-dissociated ligand migrates between three distal temporary docking sites before it subsequently rebinds to the heme iron or ultimately escapes into the solvent via a hydrophobic tunnel. The calculated energy profiles associated with the ligand migration processes are in good agreement with the experimental observations. The results highlight the importance of the Trp(G8) in regulating ligand migration in trHbO, underscoring its pivotal role in the structural and functional properties of the group II and III truncated hemoglobins.
AB - Resonance Raman studies show that the heme-bound CO in trHbO, a truncated-II hemoglobin from Mycobacterium tuberculosis, is exposed to an environment with a positive electrostatic potential. The mutation of Trp(G8), an absolutely conserved residue in group II and III truncated hemoglobins, to Phe introduces two new Fe-CO conformers, both of which exhibit reduced electrostatic potentials. Computer simulations reveal that the structural perturbation is a result of the increased flexibility of the Tyr(CD1) and Leu(E11) side chains due to the reduction of the size of the G8 residue. Laser flash photolysis studies show that the G8 mutation induces 1) the presence of two new geminate recombination phases, one with a rate faster than the time resolution of our instrument and the other with a rate 13-fold slower than that of the wild type protein, and 2) the reduction of the total geminate recombination yield from 86 to 62% and the increase in the bimolecular recombination rate by a factor of 530. Computer simulations uncover that the photo-dissociated ligand migrates between three distal temporary docking sites before it subsequently rebinds to the heme iron or ultimately escapes into the solvent via a hydrophobic tunnel. The calculated energy profiles associated with the ligand migration processes are in good agreement with the experimental observations. The results highlight the importance of the Trp(G8) in regulating ligand migration in trHbO, underscoring its pivotal role in the structural and functional properties of the group II and III truncated hemoglobins.
UR - http://www.scopus.com/inward/record.url?scp=59149085214&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=59149085214&partnerID=8YFLogxK
U2 - 10.1074/jbc.M806183200
DO - 10.1074/jbc.M806183200
M3 - Article
C2 - 19019831
AN - SCOPUS:59149085214
SN - 0021-9258
VL - 284
SP - 3106
EP - 3116
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 5
ER -