Fig. 5: The key residues of SAP05 and GATA18 for their specific recognition and degradation.

a Sequence alignment of SAP05 homologs in divergent phytoplasmas. Identical residues are marked by lightblue background. The residues that directly interact with GATA18 are numbered and denoted by black triangles. The residues that cause steric hindrance are indicated by red frames. b ITC measurements of binding affinities of wild-type and mutant WBDLa SAP05 to AtGATA18. NB, no apparent binding under our experimental conditions. c Structural comparison of the effect of the substitution of Ile84 in OY-M SAP05 by Met86 in WBDLa SAP05 on steric hindrance. The corresponding residues are shown as spheres. d Structural comparison of the effect of the substitutions of Thr68 in OY-M SAP05 by Lys70 in WBDLa SAP05 on steric hindrance. e, f Western blot analysis of the degradation of AtGATA18 using purified human 26 S proteasomes in the presence of wild-type or double mutant WBDLa SAP05. Source data are provided as a Source Data file. Representative images, n = 3. g Quantification of the percentage of retained GST-GATA18 in the degradation assay, corresponding to (e, f) (Mean ± S.E.M.; n = 3 independent experiments). h Sequence alignment of GATA domains from A. thaliana and M. quadrilineatus. Residues directly involved in SAP05 interactions in the OY-M SAP05-AtGATA18 structure are numbered and denoted by black triangles. i Three positively charged residues of AtGATA18 rather than MqGATA form salt bridge interactions. j ITC measurement of binding affinity of OY-M SAP05 to wild-type and mutant MqGATA18 (Y-R, M-K, N-R). k, l Western blot analysis of OY-M SAP05-mediated degradation of wild-type or mutant MqGATA18 (Y-R, M-K, N-R). Source data are provided as a Source Data file. Representative images, n = 3. m Quantification of the percentage of retained GST-GATA18 in the degradation assay, corresponding to (k, l) (Mean ± S.E.M.; n = 2 or 3 independent experiments).