Plants regulate their growth-inhibiting hormones (IMAGE)
Caption
Dimerization of OsGA2ox and OsDAO enhances its enzymatic activity.
Under low substrate concentration (GA4 or IAA) (left), GA2ox or DAO functions as a monomer with low enzyme activity. At high substrate concentration (right), the interface GA4 or IAA causes the formation of multimers by bridging two enzyme molecules, resulting in hyper-activation. GA4 or IAA is retained in a stable interface position, allowing two subunits to enter the active site for the next reaction without a high energy barrier. Lys or Arg is the most important amino acid for retaining GA4 or IAA and for entering the active site. Furthermore, MD simulation of OsGA2ox3 revealed the presence of a gate, allowing substrate to enter the active site and for product to exit. This gate had a hinge site composed of three amino acids, W106, C186, and V196, and was also stabilized by the interaction between R97 in subunit A and F100 in subunit D. GA4-dependent dimerization enhanced its enzymatic activity. These mechanisms are conserved in all rice GA2oxs.
Credit
S. Takehara et al. 2020
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