title: The N-terminal domain of the tomato immune protein Prf contains multiple homotypic and Pto kinase interaction sites.
abstract: Resistance to Pseudomonas syringae bacteria in tomato (Solanum lycopersicum) is conferred by the Prf recognition complex, composed of the nucleotide-binding leucine-rich repeats protein Prf and the protein kinase Pto. The complex is activated by recognition of the P. syringae effectors AvrPto and AvrPtoB. The N-terminal domain is responsible for Prf homodimerization, which brings two Pto kinases into close proximity and holds them in inactive conformation in the absence of either effector. Negative regulation is lost by effector binding to the catalytic cleft of Pto, leading to disruption of its P+1 loop within the activation segment. This change is translated through Prf to a second Pto molecule in the complex. Here we describe a schematic model of the unique Prf N-terminal domain dimer and its interaction with the effector binding determinant Pto. Using heterologous expression in Nicotiana benthamiana, we define multiple sites of N domain homotypic interaction and infer that it forms a parallel dimer folded centrally to enable contact between the N and C termini. Furthermore, we found independent binding sites for Pto at either end of the N-terminal domain. Using the constitutively active mutant ptoL205D, we identify a potential repression site for Pto in the first ∼100 amino acids of Prf. Finally, we find that the Prf leucine-rich repeats domain also binds the N-terminal region, highlighting a possible mechanism for transfer of the effector binding signal to the NB-LRR regulatory unit (consisting of a central nucleotide binding and C-terminal leucine-rich repeats).
authors: From the Research School of Biology, The Australian National University, Acton ACT 2601, Australia.
authors: Isabel Marie-Luise
authors: IM
authors: Saur
authors: From the Research School of Biology, The Australian National University, Acton ACT 2601, Australia.
authors: Brendon Francis
authors: BF
authors: Conlan
authors: From the Research School of Biology, The Australian National University, Acton ACT 2601, Australia john.rathjen@anu.edu.au.
authors: John Paul
authors: JP
authors: Rathjen
mesh_terms: D001665:Binding Sites; D004789:Enzyme Activation; D007930:Leucine; D018551:Solanum lycopersicum / Q000276:immunology* / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid; D017384:Sequence Deletion
chemical_list: D009711:Nucleotides; D010940:Plant Proteins; C084354:Pto protein, Lycopersicon; D017346:Protein Serine-Threonine Kinases; D007930:Leucine
keywords: Host-Pathogen Interaction; N-terminal Domain; NB-LRR; Prf Resistance Protein; Protein Complex; Protein Kinase; Protein Structure; Protein-Protein Interaction; Pto Serine/Threonine Kinase; Signal Transduction