Structural basis for gibberellin recognition by its receptor GID1

Area of Science:

• Plant biology
• Molecular biology
• Biochemistry

Background:

• Gibberellins (GAs) are vital plant hormones regulating development.
• The nuclear GA receptor GIBBERELLIN INSENSITIVE DWARF1 (GID1) shares structural similarity with hormone-sensitive lipases (HSLs).

Purpose of the Study:

• To elucidate the crystal structure of Oryza sativa GID1 (OsGID1) complexed with GA(4) and GA(3).
• To investigate the role of specific amino acid residues in GA binding and affinity through mutagenesis.
• To understand the evolutionary origins and adaptations of GID1 receptors.

Main Methods:

• X-ray crystallography to determine the 1.9 Å resolution structure of OsGID1 bound to GA(4) and GA(3).
• Site-directed mutagenesis of key residues identified from the crystal structure.
• GA binding assays to assess the impact of mutations on binding affinity.

Main Results:

• The OsGID1 structure revealed an alpha/beta-hydrolase fold, similar to HSLs but with an amino-terminal lid, and a GA-binding pocket corresponding to the HSL substrate-binding site.
• Mutagenesis confirmed the importance of identified residues for GA binding, as mutations resulted in significantly reduced or abolished activity.
• Specific mutations (Ile133 to Leu or Val) increased binding affinity for a hydroxylated GA, suggesting evolutionary fine-tuning.

Conclusions:

• GID1 receptors evolved from HSLs, acquiring an amino-terminal lid and adapting their GA-binding pockets.
• Evolutionary modifications in GID1's amino acid residues enhanced affinity and selectivity for bioactive GAs.
• Structural and functional analyses provide insights into the molecular mechanisms of GA perception and signaling in plants.