TY - JOUR
T1 - Docking site dynamics of ba3-cytochrome c oxidase from Thermus thermophilus
AU - Koutsoupakis, Constantinos
AU - Soulimane, Tewfik
AU - Varotsis, Constantinos
PY - 2003/9/19
Y1 - 2003/9/19
N2 - Ligand trajectories trapped within a docking site or within an internal cavity near the active site of proteins are important issues toward the elucidation of the mechanism of reaction of such complex systems, in which activity requires the shuttling of oriented ligands to and from their active site. The ligand motion within ba3-cytochrome c oxidase from Thermus thermophilus has been investigated by measuring time-resolved stepscan Fourier transform infrared difference spectra of photodissociated CO from heme a 3 at ambient temperature. Upon photodissociation, 15-20% of the CO is not covalently attached to CuB but is trapped within a docking site near the ring A of heme a3 propionate. Two trajectories of CO that are distinguished spectroscopically and kinetically (Vco = 2131 cm-1, td = 10-35 μs and vco= 2146 cm -1, td = 85 μs) are observed. At later times (t d = 110 μs) the docking site reorganizes about the CO and quickly establishes an energetic barrier that facilitates equilibration of the ligand with the protein solvent. The time-dependent shift of the CO trajectories we observe is attributed to a conformational motion of the docking site surrounding the ligand. The implications of these results with respect to the ability of the docking site to constrain ligand orientation and the reaction dynamics of the docking site are discussed herein.
AB - Ligand trajectories trapped within a docking site or within an internal cavity near the active site of proteins are important issues toward the elucidation of the mechanism of reaction of such complex systems, in which activity requires the shuttling of oriented ligands to and from their active site. The ligand motion within ba3-cytochrome c oxidase from Thermus thermophilus has been investigated by measuring time-resolved stepscan Fourier transform infrared difference spectra of photodissociated CO from heme a 3 at ambient temperature. Upon photodissociation, 15-20% of the CO is not covalently attached to CuB but is trapped within a docking site near the ring A of heme a3 propionate. Two trajectories of CO that are distinguished spectroscopically and kinetically (Vco = 2131 cm-1, td = 10-35 μs and vco= 2146 cm -1, td = 85 μs) are observed. At later times (t d = 110 μs) the docking site reorganizes about the CO and quickly establishes an energetic barrier that facilitates equilibration of the ligand with the protein solvent. The time-dependent shift of the CO trajectories we observe is attributed to a conformational motion of the docking site surrounding the ligand. The implications of these results with respect to the ability of the docking site to constrain ligand orientation and the reaction dynamics of the docking site are discussed herein.
UR - http://www.scopus.com/inward/record.url?scp=0141814916&partnerID=8YFLogxK
U2 - 10.1074/jbc.M307117200
DO - 10.1074/jbc.M307117200
M3 - Article
C2 - 12851397
AN - SCOPUS:0141814916
SN - 0021-9258
VL - 278
SP - 36806
EP - 36809
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 38
ER -