title: Role of cysteine residues and disulfide bonds in the activity of a legume root nodule-specific, cysteine-rich peptide.
abstract: The root nodules of certain legumes including Medicago truncatula produce >300 different nodule-specific cysteine-rich (NCR) peptides. Medicago NCR antimicrobial peptides (AMPs) mediate the differentiation of the bacterium, Sinorhizobium meliloti into a nitrogen-fixing bacteroid within the legume root nodules. In vitro, NCR AMPs such as NCR247 induced bacteroid features and exhibited antimicrobial activity against S. meliloti. The bacterial BacA protein is critical to prevent S. meliloti from being hypersensitive toward NCR AMPs. NCR AMPs are cationic and have conserved cysteine residues, which form disulfide (S-S) bridges. However, the natural configuration of NCR AMP S-S bridges and the role of these in the activity of the peptide are unknown. In this study, we found that either cysteine replacements or S-S bond modifications influenced the activity of NCR247 against S. meliloti. Specifically, either substitution of cysteines for serines, changing the S-S bridges from cysteines 1-2, 3-4 to 1-3, 2-4 or oxidation of NCR247 lowered its activity against S. meliloti. We also determined that BacA specifically protected S. meliloti against oxidized NCR247. Due to the large number of different NCRs synthesized by legume root nodules and the importance of bacterial BacA proteins for prolonged host infections, these findings have important implications for analyzing the function of these novel peptides and the protective role of BacA in the bacterial response toward these peptides.
authors.affiliation: School of Medicine and Dentistry, Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, United Kingdom. a.haag@live.co.uk
authors.forename: Andreas F
authors.initials: AF
authors.lastname: Haag
authors.forename: Bernhard
authors.initials: B
authors.lastname: Kerscher
authors.forename: Sergio
authors.initials: S
authors.lastname: Dall'Angelo
authors.forename: Monica
authors.initials: M
authors.lastname: Sani
authors.forename: Renato
authors.initials: R
authors.lastname: Longhi
authors.forename: Mikhail
authors.initials: M
authors.lastname: Baloban
authors.forename: Heather M
authors.initials: HM
authors.lastname: Wilson
authors.forename: Peter
authors.initials: P
authors.lastname: Mergaert
authors.forename: Matteo
authors.initials: M
authors.lastname: Zanda
authors.forename: Gail P
authors.initials: GP
authors.lastname: Ferguson
mesh_terms: D000595:Amino Acid Sequence; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D003545:Cysteine; D004220:Disulfides / Q000737:chemistry*; D046913:Medicago truncatula / Q000737:chemistry*; D026901:Membrane Transport Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010084:Oxidation-Reduction; D053204:Root Nodules, Plant / Q000737:chemistry*; D016962:Sinorhizobium meliloti / Q000187:drug effects / Q000378:metabolism
chemical_list: D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins; D004220:Disulfides; D026901:Membrane Transport Proteins; C082397:bacA protein, Rhizobium meliloti; D003545:Cysteine