The shell of a
bacterial microcompartment (or BMC) is mainly composed of hexagonal proteins,
with
pentagonal
proteins capping the vertices, similar to a soccer ball (left). Scientists have
engineered one
of these hexagonal
proteins, normally devoid of any metal center, to bind an iron-sulfur cluster
(orange and yellow
sticks, upper right). This cluster can serve as an electron relay to transfer
electrons across
the shell. Introducing this new functionality in the shell of a BMC greatly
expands
their
possibilities as custom-made bio-nanoreactors.
(Credit: Clément
Aussignargues/MSU, Cheryl Kerfeld and Markus Sutter/Berkeley Lab)
(February 5, 2016) Scientists
have for the first time reengineered a building block of a geometric
nanocompartment that occurs naturally in bacteria. They introduced a metal
binding site to its shell that will allow electrons to be transferred to and
from the compartment. This provides an entirely new functionality, greatly
expanding the potential of nanocompartments to serve as custom-made chemical
factories.
Scientists hope to tailor this new use to produce high-value
chemical products, such as medicines, on demand.
The sturdy nanocompartments, which are polyhedral shells
composed of triangle-shaped sides and resemble 20-sided dice, are formed by
hundreds of copies of just three different types of proteins. Their natural
counterparts, known as bacterial microcompartments or BMCs, encase a wide
variety of enzymes that carry out highly specialized chemistry in bacteria.
Scientists have
reengineered nanoscale polyhedral shells, which have a natural
structure
resembling the 20-sided die in this photo, to include a metal
cluster that gives
the shells a new function. (Credit: Flickr/CGPsGrey.com)
Researchers at the Department of Energy’s Lawrence Berkeley
National Laboratory (Berkeley Lab) devised synthetic shell structures derived
from those found in a rod-shaped, ocean-dwelling bacterium, Haliangium
ochraceum, and reengineered one of the shell proteins to serve as a scaffold
for an iron-sulfur cluster found in many forms of life. The cluster is known as
a “cofactor” because it can serve as a helper molecule in biochemical
reactions.
BMC-based shells are tiny, durable and naturally
self-assemble and self-repair, which makes them better-suited for a range of
applications than completely synthetic nanostructures.
This image shows a
natural atomic-scale protein structure (middle) in a polyhedral bacterial
microcompartment
(left), and an engineered structure (right) that binds an iron-sulfur cluster
(in blue), giving
it a new function. The engineered protein was produced in E. Coli bacteria—the
background image
shows a scanning electron micrograph image of E. Coli.
(Credit: Berkeley
Lab, National Institutes of Health)
“This is the first time anyone has introduced functionality
into a shell. We thought the most important functionality to introduce was the
ability to transfer electrons into or out of the shell,” said Cheryl Kerfeld, a
structural biologist at Berkeley Lab and corresponding author in this study.
Kerfeld’s research group focuses on BMCs. Kerfeld holds joint appointments with
Berkeley Lab’s Molecular Biophysics and Integrated Bioimaging (MBIB) Division,
UC Berkeley and the MSU-DOE Plant Research Laboratory at Michigan State
University (MSU).
“That greatly enhances the versatility of the types of
chemistries you can encapsulate in the shell and the spectrum of products to be
produced,” she said. “Typically, the shells are thought of as simply passive
barriers.”
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