title: Understanding the role of dynamics in the iron sulfur cluster molecular machine.
abstract: The bacterial proteins IscS, IscU and CyaY, the bacterial orthologue of frataxin, play an essential role in the biological machine that assembles the prosthetic FeS cluster groups on proteins. They form functionally binary and ternary complexes both in vivo and in vitro. Yet, the mechanism by which they work remains unclear.
  
  
  
  We carried out extensive molecular dynamics simulations to understand the nature of their interactions and the role of dynamics starting from the crystal structure of a IscS-IscU complex and the experimentally-based model of a ternary IscS-IscU-CyaY complex and used nuclear magnetic resonance to experimentally test the interface.
  
  
  
  We show that, while being firmly anchored to IscS, IscU has a pivotal motion around the interface. Our results also describe how the catalytic loop of IscS can flip conformation to allow FeS cluster assembly. This motion is hampered in the ternary complex explaining its inhibitory properties in cluster formation.
  
  
  
  We conclude that the observed 'fluid' IscS-IscU interface provides the binary complex with a functional adaptability exploited in partner recognition and unravels the molecular determinants of the reported inhibitory action of CyaY in the IscS-IscU-CyaY complex explained in terms of the hampering effect on specific IscU-IscS movements.
  
  
  
  Our study provides the first mechanistic basis to explain how the IscS-IscU complex selects its binding partners and supports the inhibitory role of CyaY in the ternary complex.
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy; Istituto Nazionale di Fisica Nucleare (INFN) sezione di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy.
authors.forename: Danilo
authors.initials: D
authors.lastname: di Maio
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy; Istituto Nazionale di Fisica Nucleare (INFN) sezione di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy.
authors.forename: Balasubramanian
authors.initials: B
authors.lastname: Chandramouli
authors.affiliation: Department of Neuroscience, Wohl Institute, King's College London, Denmark Hill Campus, London SE5, UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Yan
authors.affiliation: Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy; Istituto Nazionale di Fisica Nucleare (INFN) sezione di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy. Electronic address: giuseppe.brancato@sns.it.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Brancato
authors.affiliation: Department of Neuroscience, Wohl Institute, King's College London, Denmark Hill Campus, London SE5, UK; Immunologia Patologia Generale Department, University of Pavia, Via Ferrata, 9, 27100 Pavia, Italy. Electronic address: annalisa.pastore@crick.ac.uk.
authors.forename: Annalisa
authors.initials: A
authors.lastname: Pastore
mesh_terms: D055162:Biocatalysis; D013437:Carbon-Sulfur Lyases / Q000737:chemistry* / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D055550:Protein Stability; D017433:Protein Structure, Secondary; D055672:Static Electricity
chemical_list: D029968:Escherichia coli Proteins; D007506:Iron-Sulfur Proteins; C411665:IscU protein, E coli; D013437:Carbon-Sulfur Lyases; C080546:cysteine desulfurase
keywords: CyaY; Frataxin; Iron-sulfur cluster biogenesis; Molecular dynamics; Structure