Oriented Attachment of Cytochrome P450 Enzymes on Electrodes:
Implications for Biosensor Development
Elizabeth Schneider *, Douglas S. Clark†
*
UC Berkeley/UCSF Graduate Program in Bioengineering, University of California at Berkeley, Berkeley, CA 94720,
†
Chemical and Biomolecular Engineering, University of California at Berkeley, Berkeley, CA 94720
Tel: 510-643-8340 E-mail: ebeth@berkeley.edu
Summary: The effect of attachment chemistry and orientation on the direct and indirect
electrochemistry of Cytochrome P450 2C9 (CYP2C9) on a gold electrode is investigated
using electrochemical and surface characterization techniques.
We are developing a biosensor of mammalian cytochrome P450 enzymes (CYPs) on gold electrodes that could
be used as an initial screen for CYP activity of pharmaceuticals in development. Such a device would be useful in
the pharmaceutical industry as a tool for initial screens of drug candidates for CYP reactivity and potential drugdrug interactions. By immobilizing CYPs on an electrode (Fig 1), NADPH is no longer needed as an electron
source and catalysis can occur either via direct electrochemistry from the electrode itself, or indirect
electrochemistry using a soluble redox mediator. Attaching the P450 enzyme to the electrode in a manner that
allows for direct electron transfer to the heme co-factor buried within remains a challenge that must be overcome in
order to build an accurate biosensor. In addition, controlling the orientation of the enzyme on the electrode could
improve the electron transfer rate by ensuring that all enzyme molecules on the surface accept electrons from the
electrode in the same manner.
Fig 1: Schematic illustration of in vivo cytochrome P450 catalysis and catalysis via direct electrochemistry where the cytochrome P450 enzyme is
immobilized on a gold electrode and can be used as a biosensor
We hypothesize that orienting the P450 on the electrode surface, such that the proximal side of the heme faces
the electrode, will improve electroactivity by orienting the P450 in the same way it orients for electron transfer in
vivo, where it receives electrons from cytochrome P450 reductase (CPR), which binds on the proximal side. In this
study, we investigate oriented immobilization of a model P450 (CYP2C9) on a single gold electrode and its effects
on direct and indirect electron transfer by comparing three different immobilization methods using electrochemical
and surface characterization techniques: non-oriented and random attachment of CYP2C9 to a carboxy-terminated
self assembled monolayer (SAM), C-terminal oriented attachment of 6x His-tagged CYP2C9 to a Ni-NTA surface,
and proximal-side oriented attachment of CYP2C9 via cysteine mutations at the reductase binding site. The ability
of each immobilization method to promote direct or indirect electron transfer and produce catalytically active
CYP2C9 will elucidate the role orientation plays in enzyme electrochemistry and how it can be used to build a more
effective P450 biosensor.