Protein matrix local fluctuations and substrate binding in HRPC: A proposed dynamic electrostatic sampling method

Horseradish peroxidase C is an oxidorecluctase which catalyzes in plant roo ts the oxidation of a remarkably wide variety of aromatic compounds by H2O2 The recently available X-ray structures of the enzyme bound to aromatic su bstrates are not indicative of significant structural rearrangements as a r esult of substrate binding when compared to the structure of the unbound en zyme. Our most recent spectral hole-burning studies on HRPC fluorescent der ivatives provided direct experimental evidence indicative of different fiel ds experienced at the heme as a result of substrate binding which fan only originate in the protein matrix in which the heme is embedded. In this repo rt, we present results on modeling the fluctuations of these protein matrix electrostatic rearrangements using a combination of molecular dynamics and electrostatic conformational sampling to compare the binding of BHA and NH A to HRPC and to the derivative used in our experimental studies. Our initi al results suggest that HRPC does undergo conformational rearrangement on b inding aromatic substrates, but of an electrostatic nature, as opposed to m ajor conformational structural changes. This implies that the high versatil ity of substrate binding in horseradish peroxidase could be due to an elect rostatic dynamic selectivity mediated by small-amplitude internal protein m atrix motions. (C) 2001 John Wiley & Sons, Inc.