title: The repeat domain of the type III effector protein PthA shows a TPR-like structure and undergoes conformational changes upon DNA interaction.
abstract: Many plant pathogenic bacteria rely on effector proteins to suppress defense and manipulate host cell mechanisms to cause disease. The effector protein PthA modulates the host transcriptome to promote citrus canker. PthA possesses unusual protein architecture with an internal region encompassing variable numbers of near-identical tandem repeats of 34 amino acids termed the repeat domain. This domain mediates protein-protein and protein-DNA interactions, and two polymorphic residues in each repeat unit determine DNA specificity. To gain insights into how the repeat domain promotes protein-protein and protein-DNA contacts, we have solved the structure of a peptide corresponding to 1.5 units of the PthA repeat domain by nuclear magnetic resonance (NMR) and carried out small-angle X-ray scattering (SAXS) and spectroscopic studies on the entire 15.5-repeat domain of PthA2 (RD2). Consistent with secondary structure predictions and circular dichroism data, the NMR structure of the 1.5-repeat peptide reveals three α-helices connected by two turns that fold into a tetratricopeptide repeat (TPR)-like domain. The NMR structure corroborates the theoretical TPR superhelix predicted for RD2, which is also in agreement with the elongated shape of RD2 determined by SAXS. Furthermore, RD2 undergoes conformational changes in a pH-dependent manner and upon DNA interaction, and shows sequence similarities to pentatricopeptide repeat (PPR), a nucleic acid-binding motif structurally related to TPR. The results point to a model in which the RD2 structure changes its compactness as it embraces the DNA with the polymorphic diresidues facing the interior of the superhelix oriented toward the nucleotide bases.
authors.affiliation: Laboratório Nacional de Biociências, Centro Nacional de Pesquisa em Energia e Materiais, 13083-970, Campinas, SP, Brazil. mario.murakami@lnbio.org.br
authors.forename: Mário Tyago
authors.initials: MT
authors.lastname: Murakami
authors.forename: Mauricio Luis
authors.initials: ML
authors.lastname: Sforça
authors.forename: Jorge Luiz
authors.initials: JL
authors.lastname: Neves
authors.forename: Joice Helena
authors.initials: JH
authors.lastname: Paiva
authors.forename: Mariane Noronha
authors.initials: MN
authors.lastname: Domingues
authors.forename: André Luiz Araujo
authors.initials: AL
authors.lastname: Pereira
authors.forename: Ana Carolina de Mattos
authors.initials: AC
authors.lastname: Zeri
authors.forename: Celso Eduardo
authors.initials: CE
authors.lastname: Benedetti
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002942:Circular Dichroism; D004269:DNA, Bacterial / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D010455:Peptides