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. 2021 Jul 21;10:e66961. doi: 10.7554/eLife.66961

Figure 9. Model of molecular convergence of Pikp-1 and Pikm-1 towards AVR-PikD binding at high affinity.

(A) The heavy metal-associated (HMA) domains of Pikp-1 and Pikm-1 receptors have convergently evolved through distinct evolutionary and biochemical paths to bind AVR-PikD with high affinity. The Pikp-HMA domain evolved through the AV-VE adaptations in the IAQVV/LVKIE region, whereas Pikm-HMA domain acquired the ANK-VKE mutations in the MKANK/EMVKE region. Schematic representations of the HMA–AVR-PikD structures, adapted from De la Concepcion et al., 2018, are presented with selected side chains shown as sticks and labelled; the colours of the residue labels match colours of the respective molecules. Dashed lines stand for hydrogen bonds or salt bridges. (B) The protein sequence alignment between Pikp-HMA, Pikm-HMA, and ancestral HMA (ancHMA), with relevant amino acids marked. (C) We propose a model in which the HMA effector target integrated into Pik-1 to bait the recognition of an unknown effector. Throughout evolution the Pik-1 receptor and its integrated HMA domain diversified and led to the emergence of the Pikp-1 and Pikm-1 allelic variants that bind newly emerged AVR-PikD effector.

Figure 9.

Figure 9—figure supplement 1. The Val-230-Glu mutation within the LVKIE region of ancestral HMA (ancHMA) enhances interaction with AVR-PikD through hydrogen bond formation.

Figure 9—figure supplement 1.

(A) Schematic representation of the structure of ancHMALVKIE complexed with the AVR-PikD effector. The molecules are shown as ribbons with selected side chains presented as sticks and labelled; the colours of the residue labels match the colours of the respective molecules. The molecular surfaces of AVR-PikD (pink) and LVKIE residues (blue) within ancHMALVKIE are also shown. Dashed lines represent hydrogen bonds or salt bridges formed between the two molecules. (B) Superimposition of the ancHMALVKIE structure and the ancHMA homology model (grey) in complex with AVR-PikD. (C) Close-up views of the IAQVV/LVKIE region of ancHMALVKIE (green and blue) and ancHMA (green) showcasing differences in binding to AVR-PikD (pink). The selected residues involved in binding are labelled with labels matching the colours of the corresponding molecules. The LVKIE residues are labelled with single-letter amino acid symbols—Ile/Leu-221 (I/L), Ala/Val-222 (A/V), Gln/Lys-228 (Q/K), Val/Ile-229 (V/I), Val/Glu-230 (V/E) for ancHMA/ancHMALVKIE; and Ile-222 (I), Ala-223 (A), Gln-231 (Q), Val-232 (V), Val-233 (V) for Pikm-HMA. Dashed lines represent hydrogen bonds or salt bridges formed between the two molecules.