Enantiomer-specific accumulation, biotransformation of HBCDs in maize and the selective molecular mechanisms

Accumulation, bioisomerization and metabolization of individual hexabromocyclododecane (HBCD) enantiomers in maize (Zea mays L.) were investigated. Molecular interactions of HBCD enantiomers with plant isozymes were further... [ view full abstract ]

Accumulation, bioisomerization and metabolization of individual hexabromocyclododecane (HBCD) enantiomers in maize (Zea mays L.) were investigated. Molecular interactions of HBCD enantiomers with plant isozymes were further characterized by homology modeling combined with molecular docking. The (−)α-, (−)β- and (+)γ-HBCDs accumulated significantly higher in maize than their corresponding antipodes. Bioisomerization from (±)β- / (±)γ-HBCD to (−)α-HBCD was frequently observed, and (−)γ-HBCD was most easily converted with bioisomerization efficiency of 90.47 ± 8.24%. Mono- and dihydroxyl HBCDs, debrominated metabolites of pentabromocyclododecenes (PBCDs) and tetrabromocyclododecenes (TBCDs), and HBCD-GSH adducts were detected in maize roots. Patterns of hydroxylated and debrominated metabolites were significant different among HBCD enantiomers. Three pairs of HBCD enantiomers selectively bound into the active sites and interacted with specific residues of maize isozymes of CYP71C3v2 and GST31. (+)α-, (−)β- and (−)γ-HBCDs preferentially bound to CYP71C3v2, while (−)α-, (−)β- and (+)γ-HBCD had strong affinities to GST31, which were consistent with the experimental observations that (+)α-, (−)β- and (−)γ-HBCDs were more easily hydroxylated , and (−)α-, (−)β- and (+)γ-HBCDs were more easily isomerized and debrominated by maize compared to their enantiomeric pairs. This study for the first time provided both experimental and theoretical evidences for enantiomer-specific biotic processes of HBCD in maize.