Following ligand migration pathways from picoseconds to milliseconds in type II truncated hemoglobin from Thermobifida Fusca

A. MARCELLI; S. ABBRUZZETTI; J.P. BUSTAMANTE; A. FEIS; A. BONAMORE; A. BOFFI; C. GELLINI; P.R. SALVI; D.A. ESTRIN; S. BRUNO; C VIAPPIANI; P. FOGGI

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2012 vol. 7 p. 39884 - 39884

1932-6203

CO recombination kinetics has been investigated in the type II truncated hemoglobin from Thermobifida fusca (Tf-trHb) overmore than 10 time decades (from 1 ps to ,100 ms) by combining femtosecond transient absorption, nanosecond laserflash photolysis and optoacoustic spectroscopy. Photolysis is followed by a rapid geminate recombination with a timeconstant of ,2 ns representing almost 60% of the overall reaction. An additional, small amplitude geminate recombinationwas identified at ,100 ns. Finally, CO pressure dependent measurements brought out the presence of two transient speciesin the second order rebinding phase, with time constants ranging from ,3 to ,100 ms. The available experimentalevidence suggests that the two transients are due to the presence of two conformations which do not interconvert withinthe time frame of the experiment. Computational studies revealed that the plasticity of protein structure is able to define abranched pathway connecting the ligand binding site and the solvent. This allowed to build a kinetic model capable ofdescribing the complete time course of the CO rebinding kinetics to Tf-trHb.