Computational studies on the catalytic mechanism of phosphoketolase

Phosphoketolase (PK) is a thiamine diphosphate (THDP) dependent enzyme which plays key roles in the metabolism of heterofermentative bacteria. By using density functional theory (DFT) method, the catalytic mechanism of PK has been studied on simplified models. The calculation results indicate that the formation of 2-α,β-dihydroxyethylidene-THDP (DHETHDP) and erythrose-4-phosphate (E4P) involves one C–C bond formation and one C–C bond cleavage process. Each C–C bond formation or cleavage is always accompanied by a proton transfer in a concerted but asynchronous way. The dehydration process in the reaction of PK is distinct from that of other THDP-dependent enzymes. The Keto–Enol tautomerism process is assisted with a mediator His553. His64, His553 and His97 are found to have the function to stabilize the transition states and intermediates. His64 is a better candidate of B1 catalyst. His553 acts as a proton donor to protonate the carbonyl oxygen, and plays intermediary role in the Keto–Enol tautomerism process. His97 is the probable B2 catalyst in the dehydration process.