Identification of triphosphoribosyl‐dephospho‐CoA as precursor of the citrate lyase prosthetic group

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Abstract
The γ‐subunit of citrate lyase (EC 4.1.3.6) contains the prosthetic group 2′‐(5″‐phosphoribosyl)‐3′‐dephospho‐CoA and serves as an acyl carrier protein (ACP). We recently showed that in Escherichia coli the proteins CitG and CitX are essential for holo‐ACP synthesis and provided evidence that CitG catalyzes the formation of a prosthetic group precursor from ATP and dephospho‐CoA, which is subsequently attached via phosphodiester linkage to apo‐ACP by CitX. Here we prove that CitG indeed catalyzes the conversion of ATP and dephospho‐CoA to adenine and 2′‐(5″‐triphosphoribosyl)‐3′‐dephospho‐CoA, the predicted precursor of the prosthetic group. Furthermore, this precursor was transferred by CitX to apo‐ACP, yielding holo‐ACP. Thus, our proposed mechanism for holo‐ACP synthesis could be verified.