title: Structural studies of Streptococcus pyogenes streptolysin O provide insights into the early steps of membrane penetration.
abstract: Cholesterol-dependent cytolysins (CDCs) are a large family of bacterial toxins that exhibit a dependence on the presence of membrane cholesterol in forming large pores in cell membranes. Significant changes in the three-dimensional structure of these toxins are necessary to convert the soluble monomeric protein into a membrane pore. We have determined the crystal structure of the archetypical member of the CDC family, streptolysin O (SLO), a virulence factor from Streptococcus pyogenes. The overall fold is similar to previously reported CDC structures, although the C-terminal domain is in a different orientation with respect to the rest of the molecule. Surprisingly, a signature stretch of CDC sequence called the undecapeptide motif, a key region involved in membrane recognition, adopts a very different structure in SLO to that of the well-characterized CDC perfringolysin O (PFO), although the sequences in this region are identical. An analysis reveals that, in PFO, there are complementary interactions between the motif and the rest of domain 4 that are lost in SLO. Molecular dynamics simulations suggest that the loss of a salt bridge in SLO and a cation-pi interaction are determining factors in the extended conformation of the motif, which in turn appears to result in a greater flexibility of the neighboring L1 loop that houses a cholesterol-sensing motif. These differences may explain the differing abilities of SLO and PFO to efficiently penetrate target cell membranes in the first step of toxin insertion into the membrane.
authors: ACRF Rational Drug Discovery Centre, Biota Structural Biology Laboratory, St. Vincent's Institute of Medical Research, Fitzroy, Victoria 3065, Australia.
authors: Susanne C
authors: SC
authors: Feil
authors: ACRF Rational Drug Discovery Centre, Biota Structural Biology Laboratory, St. Vincent's Institute of Medical Research, Fitzroy, Victoria 3065, Australia.
authors: David B
authors: DB
authors: Ascher
authors: Victorian Life Sciences Computation Initiative, The University of Melbourne, Parkville, Victoria 3010, Australia.
authors: Michael J
authors: MJ
authors: Kuiper
authors: Department of Microbiology and Immunology, University of Oklahoma, Health Sciences Center, Oklahoma City, OK 73104, USA.
authors: Rodney K
authors: RK
authors: Tweten
authors: ACRF Rational Drug Discovery Centre, Biota Structural Biology Laboratory, St. Vincent's Institute of Medical Research, Fitzroy, Victoria 3065, Australia; Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, Victoria 3010, Australia. Electronic address: mparker@svi.edu.au.
authors: Michael W
authors: MW
authors: Parker
mesh_terms: D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001427:Bacterial Toxins / Q000737:chemistry; D002462:Cell Membrane / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D018360:Crystallography, X-Ray; D006460:Hemolysin Proteins / Q000737:chemistry; D008958:Models, Molecular; D011487:Protein Conformation; D055503:Protein Multimerization; D013297:Streptococcus pyogenes / Q000737:chemistry / Q000472:pathogenicity*; D013301:Streptolysins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D006460:Hemolysin Proteins; D013301:Streptolysins; C025964:streptolysin O; C020452:Clostridium perfringens theta-toxin; D002784:Cholesterol
keywords: ALO; CDC; ILY; NHMRC; National Health and Medical Research Council of Australia; PFO; SLO; SLY; X-ray crystallography; anthrolysin; cholesterol-dependent cytolysin; conformational change; intermedilysin; membrane insertion; molecular dynamics simulations; perfringolysin O; pore-forming toxins; streptolysin O; suilysin