Download Artificial Enzyme Design, written by Emily Coyte

Ross Anderson
Artificial Enzyme Design and Assembly
With proteins as with novels, it’s one thing to understand and another matter entirely to be
able to successfully create your own. Our knowledge of proteins and the relationship
between structure and function has improved so much in the past fifty years that we are right
now at an exciting transition between understanding protein structure and designing our
own.
From Taq polymerase in PCR to restriction enzymes in genetic modification, enzymes have
been used outside of their natural context for decades, but the range for utility is limited by
what evolution on this planet has given us. Enhancing that range with new, man-made
proteins has huge potential for human health and understanding.
Two options present themselves: adapt some of the huge diversity of proteins found in
nature, or create completely novel ones from first principles. Natural enzymes are exquisite
machines evolved over millions of years to fill specific niches within a living organism. As
well as core catalytic roles, each enzyme must be able to interact with dozens of other
molecules and respond to multiple signals to allow the organism to survive in a changing
natural environment. These additional features are unhelpful baggage to those seeking to
manipulate the enzyme for other functions, but the high interdependence of amino acids
within natural proteins makes modification very challenging. Improving one aspect of
enzyme function could easily destroy another, perhaps causing it to aggregate.
The approach of the Anderson lab uses an alternative route - not adapting pre-existing
enzymes, but designing them from scratch for eventual use as diverse and specific catalytic
tools. The proteins they work with are called maquettes; “rough drafts” of fully functional new
enzymes. These are mostly based on simple four-helix bundles where the each amino acid
has a simple and clearly defined role, which may include the binding of cofactors at the
centre of the bundle. The tractability of each amino acid bestow control over the maquette’s
fundamental properties in a way simply not possible in natural proteins.
As well as sculpting these maquettes into a wide range of fully synthetic enzymes, an
exciting challenge for the Anderson lab is usefully integrating them into living organisms.
They have already successfully designed a maquette which is expressed, translocated and
post-translationally modified by natural machinery of E. coli, converting a non-covalent heme
B cofactor into covalently ligated heme C. This was a phenomenal proof-of-concept and the
first example of a man-made protein to be fully packaged with a natural cofactor in vivo.
Removing heme dissociation in this way has greatly facilitated study of the maquette’s
structure and possible functions with an aim of eventually substituting them into natural
biochemical pathways such as respiration or photosynthesis.
The maquettes are capable of binding two cofactors with different redox potentials
simultaneously which permits electron transfer across the protein. The lab has demonstrated
this in a maquette with one heme B and one heme C which could be incorporated into a
respiratory pathway. They also found that replacing the iron in heme C with zinc produced a
maquette with light-activated electron transfer, a key process of photosynthesis. Combining
the design of man-made proteins with efficient expression in cells could open up huge new
avenues including improved targeted therapies and environmentally-friendly fuel systems.