title: Coiled-coil destabilizing residues in the group A Streptococcus M1 protein are required for functional interaction.
abstract: The sequences of M proteins, the major surface-associated virulence factors of the widespread bacterial pathogen group A Streptococcus, are antigenically variable but have in common a strong propensity to form coiled coils. Paradoxically, these sequences are also replete with coiled-coil destabilizing residues. These features are evident in the irregular coiled-coil structure and thermal instability of M proteins. We present an explanation for this paradox through studies of the B repeats of the medically important M1 protein. The B repeats are required for interaction of M1 with fibrinogen (Fg) and consequent proinflammatory activation. The B repeats sample multiple conformations, including intrinsically disordered, dissociated, as well as two alternate coiled-coil conformations: a Fg-nonbinding register 1 and a Fg-binding register 2. Stabilization of M1 in the Fg-nonbinding register 1 resulted in attenuation of Fg binding as expected, but counterintuitively, so did stabilization in the Fg-binding register 2. Strikingly, these register-stabilized M1 proteins gained the ability to bind Fg when they were destabilized by a chaotrope. These results indicate that M1 stability is antithetical to Fg interaction and that M1 conformational dynamics, as specified by destabilizing residues, are essential for interaction. A "capture-and-collapse" model of association accounts for these observations, in which M1 captures Fg through a dynamic conformation and then collapses into a register 2-coiled coil as a result of stabilization provided by binding energy. Our results support the general conclusion that destabilizing residues are evolutionarily conserved in M proteins to enable functional interactions necessary for pathogenesis.
authors: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093;
authors: Chelsea M
authors: CM
authors: Stewart
authors: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093;
authors: Cosmo Z
authors: CZ
authors: Buffalo
authors: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093;
authors: J Andrés
authors: JA
authors: Valderrama
authors: Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093;
authors: Anna
authors: A
authors: Henningham
authors: Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093;
authors: Jason N
authors: JN
authors: Cole
authors: Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093; Skaggs School of Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA 92093.
authors: Victor
authors: V
authors: Nizet
authors: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093; pghosh@ucsd.edu.
authors: Partho
authors: P
authors: Ghosh
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry* / Q000378:metabolism; D000942:Antigens, Bacterial / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005340:Fibrinogen / Q000737:chemistry* / Q000378:metabolism; D015870:Gene Expression; D005822:Genetic Vectors / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D009154:Mutation; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D054730:Protein Interaction Domains and Motifs; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013297:Streptococcus pyogenes / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; D011994:Recombinant Proteins; C014689:streptococcal M protein; D005340:Fibrinogen
keywords: M protein; coiled coil; dynamics; fibrinogen; group A Streptococcus