Stopped-Flow Studies of the Reduction of the Copper Centers Suggest a Bifurcated Electron Transfer Pathway in Peptidylglycine Monooxygenase

Abstract

PHM is a dicopper enzyme that plays a vital role in the amidation of glycine extended pro-peptides. One of the crucial aspects of its chemistry is the transfer of two electrons from an electron-storing and transferring site (CuH) to the oxygen binding site and catalytic center (CuM) over a distance of 11 Å during one catalytic turnover event. Here we present our studies on the first electron transfer step (reductive phase) in the WT PHM as well as its variants. Stopped-flow was used to record the reduction kinetic traces using the chromophoric agent DMPD as the reductant. The reduction was found to be biphasic in the WT PHM with an initial fast phase (17.2s−1) followed by a much slower phase (0.46s−1). We were able to ascribe the fast and slow phase to the CuH and CuM-sites respectively by making use of the H242A and H107H108A mutants which only contain the CuH-site and CuM-site respectively. In the absence of substrate the redox potentials determined by cyclic voltammetry were 270 mV (CuH-site) and −15 mV (CuM-site), but binding of substrate (Ac-YVG) was found to alter both potentials so that they converged to a common value of 83 mV. Substrate binding also accelerated the slow reductive phase by ~10 fold, an effect that could be explained at least partially by the equalization of the reduction potential of the copper centers. Studies on H108A showed that the ET to the CuM-site is blocked, highlighting the role of the H108 ligand as a component of the reductive ET pathway. Strikingly, the rate of reduction of the H172A variant was unaffected despite the rate of catalysis being three orders of magnitude less than that of the WT PHM. These studies strongly indicate that the reductive phase and catalytic phase ET pathways are different and suggest a bifurcated ET pathway in PHM. We propose that H172 and Y79 form part of an alternate pathway for the catalytic phase ET while the H108 ligand along with the water molecules and substrate form the reductive phase ET pathway.

Bioinspired Synthesis of Cu2+‐Modified Covalent Triazine Framework: A New Highly Efficient and Promising Peroxidase Mimic

“…Notably, copper ions are commonly found as the active sites in natural enzymes, such as laccase and amine oxidases. In this context, excellent works by Lu and co‐workers showed that copper is the element of choice for the design and synthesis of enzymes; however, the skeleton of these modified Cu‐containing enzymes still consists of proteins or amino acids. Thus, the development of new artificial protein‐like ligands containing anchored copper ions to mimic the activity of native enzymes is of great interest.…”

“…In this context,e xcellent works by Lu [20][21][22][23] and co-workerss howed that copperi st he element of choice for the design and synthesis of enzymes; however,t he skeleton of these modified Cu-containing enzymes still consists of proteins or amino acids. In this context,e xcellent works by Lu [20][21][22][23] and co-workerss howed that copperi st he element of choice for the design and synthesis of enzymes; however,t he skeleton of these modified Cu-containing enzymes still consists of proteins or amino acids.…”

Rational Design of a Histidine–Methionine Site Modeling the M-Center of Copper Monooxygenases in a Small Metallochaperone Scaffold

“…The data were fit by non-linear regression to a rate equation which describes the process as a combination of fast and slow pseudo first order reactions and is identical to that used previously to analyze the DMPD reduction of the WT PHM. 81 A t = A 0 + A 1 1 − e −k 1…”

Effects of copper occupancy on the conformational landscape of peptidylglycine α-hydroxylating monooxygenase

“…The structures of the PHM and PAL domains of rat PAM, alone and in complexes with substrates, inhibitors, and other ligands, have been determined 11 – 15 . Other techniques used to study PHM have ranged from kinetics and kinetic isotope effect measurements 16 – 20 , to inhibitor design 21 – 24 , spectroscopy 25 – 29 including X-ray absorption spectroscopy (XAS) 17 , 30 – 33 , and computational studies 11 , 34 – 36 . These studies have provided significant insights into the mechanism of both domains, especially of PHM.…”