BRI1 is a Brassinosteroid recognizing plasma membrane bound LRR receptor. BRI1 can recognize the variety of the braasinosteroid derivatives. To understand the mechanism of BR binding to BRI1 the authors in this paper studied the crystal structure of BRI1 in the presence and absence of active form of BRs, Brassinolide.

BRI1 exists as a monomer consisting 25 LRRs packed into helical solenoid structure. Contrasting to the usual horse shoe shaped structure of other LRRs; BRI1 is different as it is twisted. BL binds to the hydrophobic surface groove between the insertion domain and concave side of the solenoid of BRI1.two short segment; residue 590-595, 644- 646 from the insertional domain contain the interpretable electrone density in the presence of the BL but not in absence of BL. Overal structure of BRI1 is not changed during BL binding. Brassinolide had no effect on the BRI1homodmezation as revealed by the unchanged molecular weight of BRI1 in gel filtration assay and protoplast experiment. The homodimerization seen in the crystallography may be due to crystal packing only.

 The mechanism of BL recognition by BRI1 is induced fit mechanism. The local structure rearrangement in the two loops linking the insertional domain and LRR structure occurs as BL bind resulting the formation of surface groove for BL binding on BRI1.