PduL Is an Evolutionarily Distinct Phosphotransacylase Involved in B 12 -Dependent 1,2-Propanediol Degradation by Salmonella enterica Serovar Typhimurium LT2

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Abstract
Salmonella enterica degrades 1,2-propanediol (1,2-PD) in a coenzyme B 12 -dependent manner. Previous enzymatic assays of crude cell extracts indicated that a phosphotransacylase (PTAC) was needed for this process, but the enzyme involved was not identified. Here, we show that the pduL gene encodes an evolutionarily distinct PTAC used for 1,2-PD degradation. Growth tests showed that pduL mutants were unable to ferment 1,2-PD and were also impaired for aerobic growth on this compound. Enzyme assays showed that cell extracts from a pduL mutant lacked measurable PTAC activity in a background that also carried a pta mutation (the pta gene was previously shown to encode a PTAC enzyme). Ectopic expression of pduL corrected the growth defects of a pta mutant. PduL fused to eight C-terminal histidine residues (PduL-His 8 ) was purified, and its kinetic constants were determined: the V max was 51.7 ± 7.6 μmol min −1 mg −1 , and the K m values for propionyl-PO 4 2− and acetyl-PO 4 2− were 0.61 and 0.97 mM, respectively. Sequence analyses showed that PduL is unrelated in amino acid sequence to known PTAC enzymes and that PduL homologues are distributed among at least 49 bacterial species but are absent from the Archaea and Eukarya .

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