(R)-1-hydroxy-2-aminoethylphosphonate ammonia-lyase, a new PLP-dependent enzyme involved in bacterial phosphonate degradation

Phosphonates contain a particularly stable carbon-phosphorus bond, yet a number of microorganisms possess pathways to degrade these molecules and use them as source of phosphorus. One example is the widespread hydrolytic route for the breakdown of 2-aminoethylphosphonate (AEP). In this pathway, the aminotransferase PhnW initially converts AEP into phosphonoacetaldehyde (PAA), which is then cleaved by the hydrolase PhnX to yield acetaldehyde and phosphate. This work focuses on a novel enzyme (hereby termed PbfA), which is often encoded in bacterial gene clusters containing the phnW-phnX combination. Although PbfA is annotated as a transaminase, we report that it catalyzes an elimination reaction on the naturally occurring compound (R)-1-hydroxy-2-aminoethylphosphonate (R-HAEP). The reaction releases ammonia and generates PAA, which can be subsequently hydrolyzed by PhnX. Overall, the PbfA reaction represents a frequent accessory branch in the hydrolytic pathway for AEP degradation, which expands the scope and versatility of the pathway itself.