Solution structure of the major (Spy0128) and minor (Spy0125 and Spy0130) pili subunits from Streptococcus pyogenes
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Adhesion of the serotype M1 Streptococcus pyogenes strain SF370 to human tonsil explants and cultured keratinocytes requires extended polymeric surface structures called pili. In this important human pathogen, pili are assembled from three protein subunits: Spy0125, Spy0128 and Spy0130 through the action of sortase enzymes. For this study, the structural properties of these pili proteins have been investigated in solution. Spy0125 and Spy0128 display characteristics of globular, folded proteins. Circular dichroism suggests a largely β-sheet composition for Spy0128 and Spy0125; Spy0130 appears to contain little secondary structure. Each of the proteins adopts a monodisperse, monomeric state in solution as assessed by analytical ultracentrifugation. Further, small-angle X-ray scattering curves for Spy0125, Spy0128 and Spy0130 suggest each protein adopts an elongated shape, likely comprised of two domains, with similar maximal dimensions. Based on the scattering data, dummy atom models of each of the pili subunits have been reconstructed ab initio. This study provides the first insights into the structure of Streptococcus pyogenes minor pili subunits, and possible implications for protein function are discussed.
KeywordsPili subunits Circular dichroism Analytical ultracentrifugation Small-angle X-ray scattering Dummy atom model Structural disorder
This work was supported, in part, by MRC project grant G0400849 (to MAK) and a Royal Society University Research Fellowship to Mark J. Banfield. Jonathan A. Pointon is supported by a studentship from the Medical Research Council (MRC), UK. Alexandra S. Solovyova and Mark J. Banfield are grateful to Newcastle University for funding. The authors thank the Daresbury-SRS (UK) and the EMBL-Hamburg Outstation (Germany) for the provision of beamtime and the expert assistance of beamline staff and software developers during data acquisition and data treatment [specifically Günter Grossmann (SRS), Dmitri Svergun and Peter Konarev (EMBL-DESY)].
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