title: Ligand migration in the truncated hemoglobin-II from Mycobacterium tuberculosis: the role of G8 tryptophan.
abstract: 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 photodissociated 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.
authors.affiliation: Catalan Institution for Research and Advanced Studies, Life Science Program, Barcelona Supercomputing Center, Edificio Nexus II, Barcelona 08028, Spain. Electronic address: victor.guallar@bsc.es.
authors.forename: Victor
authors.initials: V
authors.lastname: Guallar
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: Changyuan
authors.initials: C
authors.lastname: Lu
authors.affiliation: Catalan Institution for Research and Advanced Studies, Life Science Program, Barcelona Supercomputing Center, Edificio Nexus II, Barcelona 08028, Spain.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Borrelli
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Egawa
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461. Electronic address: syeh@aecom.yu.edu.
authors.forename: Syun-Ru
authors.initials: SR
authors.lastname: Yeh
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry; D020134:Catalytic Domain; D003198:Computer Simulation; D006454:Hemoglobins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000378:metabolism*; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D014364:Tryptophan / Q000378:metabolism*
chemical_list: D006454:Hemoglobins; D008024:Ligands; D002248:Carbon Monoxide; D014364:Tryptophan