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![[Figure 4]](jb5072fig4mag.jpg)
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Figure 4
The ectodomains of SRF6 and SRF7 do not display high-affinity binding to Arabidopsis BIR receptor pseudokinases or to SERK3. (a) Grating-coupled interferometry (GCI) binding kinetics of BIR1, BIR2, BIR3 and SERK3 versus SRF6 and SRF7. The known, ligand-independent interaction between BIRs and SERK3 served as a positive control. Sensorgrams are shown with raw data in red and their respective fits in black. Binding kinetics were analysed by a 1:1 binding model. Tabular summaries of kinetic parameters are shown alongside (ka, association rate constant; kd, dissociation rate constant; KD, dissociation constant; n.d., no detectable binding). (b) Key residues required for BR hormone binding and BRI1 receptor association in SERK3 are not conserved in SRF6. A structural superposition of the SRF6 (blue ribbon diagram) and SERK3 (orange, PDB entry 8wec) ectodomains is shown (r.m.s.d. of ∼0.95 Å comparing 175 corresponding Cα atoms). Phe60 and His61 in SERK3, which are part of the steroid hormone binding site in the BRI1–SERK complex, correspond to Arg64 and Gly65 in SRF6, respectively. Tyr100 and Tyr124 in SERK3 involved in the binding of the BRI1 LRR domain correspond to Ser104 and Ala126 in SRF6. (c) Residues in BIR receptor pseudokinases involved in the interaction with SERK proteins are not conserved in SRF6. A structural superposition of SRF6 and BIR2 (purple, PDB entry 6fg7, r.m.s.d. of ∼0.92 Å comparing 113 corresponding Cα atoms) reveals that the distal SERK binding surface in BIR2 involving Trp73, Phe152 and Arg176 is not conserved in SRF6. |
![[Figure 4]](jb5072fig4.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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