Stepwise visualization of membrane pore formation by suilysin, a bacterial cholesterol-dependent cytolysin
journal contributionposted on 11.03.2015, 09:52 by C. Leung, N. V. Dudkina, N. Lukoyanova, A. W. Hodel, I. Farabella, A. P. Pandurangan, Nasrin Jahan, Mafalda Pires Damaso, D. Osmanovic, C. F. Reboul, M. A. Dunstone, Peter W. Andrew, Rana Lonnen, M. Topf, H. R. Saibil, B. W. Hoogenboom
Membrane attack complex/perforin/cholesterol-dependent cytolysin (MACPF/CDC) proteins constitute a major superfamily of pore-forming proteins that act as bacterial virulence factors and effectors in immune defence. Upon binding to the membrane, they convert from the soluble monomeric form to oligomeric, membrane-inserted pores. Using real-time atomic force microscopy (AFM), electron microscopy (EM), and atomic structure fitting, we have mapped the structure and assembly pathways of a bacterial CDC in unprecedented detail and accuracy, focussing on suilysin from Streptococcus suis. We show that suilysin assembly is a noncooperative process that is terminated before the protein inserts into the membrane. The resulting ring-shaped pores and kinetically trapped arc-shaped assemblies are all seen to perforate the membrane, as also visible by the ejection of its lipids. Membrane insertion requires a concerted conformational change of the monomeric subunits, with a marked expansion in pore diameter due to large changes in subunit structure and packing.