29 research outputs found
A Synthetic Alternative to Canonical One-Carbon Metabolism
One-carbon metabolism
is an ubiquitous metabolic pathway that encompasses
the reactions transferring formyl-, hydroxymethyl- and methyl-groups
bound to tetrahydrofolate for the synthesis of purine nucleotides,
thymidylate, methionine and dehydropantoate, the precursor of coenzyme
A. An alternative cyclic pathway was designed that substitutes 4-hydroxy-2-oxobutanoic
acid (HOB), a compound absent from known metabolism, for the amino
acids serine and glycine as one-carbon donors. It involves two novel
reactions, the transamination of l-homoserine and the transfer
of a one-carbon unit from HOB to tetrahydrofolate releasing pyruvate
as coproduct. Since canonical reactions regenerate l-homoserine
from pyruvate by carboxylation and subsequent reduction, every one-carbon
moiety made available for anabolic reactions originates from CO<sub>2</sub>. The HOB-dependent pathway was established in an <i>Escherichia coli</i> auxotroph selected for prototrophy using
long-term cultivation protocols. Genetic, metabolic and biochemical
evidence support the emergence of a functional HOB-dependent one-carbon
pathway achieved with the recruitment of the two enzymes l-homoserine transaminase and HOB-hydroxymethyltransferase and of
HOB as an essential metabolic intermediate. <i>Escherichia coli</i> biochemical reprogramming was achieved by minimally altering canonical
metabolism and leveraging on natural selection mechanisms, thereby
launching the resulting strain on an evolutionary trajectory diverging
from all known extant species