Mononuclear, non-heme Fe(II), alpha-ketoglutarate (αKG) dependent biosynthetic enzymes can activate C-H bonds and catalyze a variety of reactions such as hydroxylation, halogenation and stereoinversion. In addition to the diversity of function, the fact that these enzymes catalyze such chemical transformations, otherwise challenging in industrial settings, under mild conditions and with precise selectivity places them at the forefront of chemical and biological research. SyrB2, an aliphatic halogenase, is one of the most extensively studied members of this family of enzymes and its propensity towards halogenation instead of hydroxylation has intrigued scientists for years, primarily because it shares many similarities with related hydroxylases. The endeavor to understand this halogenation bias in SyrB2 has been made more difficult by the fact that it reacts only on substrates delivered to its Fe(II) active site via a phosphopantetheine arm attached to a carrier protein SyrB1.Thus, in lieu of accurate structural models, largely due to difficulty in co-crystallizing the SyrB2/SyrB1 complex, recent experimental studies and simulations have attempted to investigate the reason behind the intriguing reaction selectivity of SyrB2. One hypothesis, recently corroborated by results of a hyperfine sublevel correlation (HYSCORE) spectroscopy study on SyrB2, is that substrate position relative to the Fe(II) active site controls the reaction outcome. In order to further investigate this hypothesis, we have employed long-time classical molecular dynamics and large-scale QM/MM calculations on the SyrB2/SyrB1 complex. We have identified some unique substrate-protein interactions that promote halogenation and suppress hydroxylation. Our simulations have also allowed us to resolve, to a certain degree, the uncertainty in literature regarding the three possible coordination isomers of the Fe(II) active site in SyrB2. Overall, we believe our computational toolkit can play a unique role in overhauling current experimental limitations and contributing new, fundamental insights into the diverging reactivity of other related non-heme Fe(II)/ αKG dependent enzymes.

Computational investigation of reaction selectivity in non-heme Fe(II) and alphaketoglutarate dependent halogenase SyrB2

2019 Fall National Meeting

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