1 research outputs found
Identification and Characterization of Solvent-Filled Channels in Human Ferrochelatase
Ferrochelatase catalyzes the formation of protoheme from
two potentially
cytotoxic products, iron and protoporphyrin IX. While much is known
from structural and kinetic studies on human ferrochelatase of the
dynamic nature of the enzyme during catalysis and the binding of protoporphyrin
IX and heme, little is known about how metal is delivered to the active
site and how chelation occurs. Analysis of all ferrochelatase structures
available to date reveals the existence of several solvent-filled
channels that originate at the protein surface and continue to the
active site. These channels have been proposed to provide a route
for substrate entry, water entry, and proton exit during the catalytic
cycle. To begin to understand the functions of these channels, we
investigated in vitro and in vivo a number of variants that line these
solvent-filled channels. Data presented herein support the role of
one of these channels, which originates at the surface residue H240,
in the delivery of iron to the active site. Structural studies of
the arginyl variant of the conserved residue F337, which resides at
the back of the active site pocket, suggest that it not only regulates
the opening and closing of active site channels but also plays a role
in regulating the enzyme mechanism. These data provide insight into
the movement of the substrate and water into and out of the active
site and how this movement is coordinated with the reaction mechanism