Formation of pre-pore complexes of pneumolysin is accompanied by a decrease in short-range order of lipid molecules throughout vesicle bilayers

• Published in: Scientific reports 2020-03, Vol.10 (1), p.4585-4585, Article 4585
• Main Authors: Faraj, Bayan H. A., Collard, Liam, Cliffe, Rachel, Blount, Leanne A., Lonnen, Rana, Wallis, Russell, Andrew, Peter W., Hudson, Andrew J.
• Format: Article
• Language: English
• Subjects: 140/125; 140/133; 631/57/2270; 639/638; 9/10; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Cholesterol; Cholesterol - chemistry; Cholesterol - metabolism; Hemolysis; Humanities and Social Sciences; Lipid bilayers; Lipid Bilayers - chemistry; Lipid Bilayers - metabolism; Lipid rafts; Lipids; Microfluidic Analytical Techniques; Microfluidics; Models, Molecular; multidisciplinary; Mutation; Optical Tweezers; Packing; Pneumolysin; Protein Binding; Proteins; Rotational diffusion; Science; Science (multidisciplinary); Spectrum Analysis, Raman; Streptococcus pneumoniae - metabolism; Streptolysins - chemistry; Streptolysins - genetics; Streptolysins - metabolism; Unilamellar Liposomes - chemistry; Unilamellar Liposomes - metabolism
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-020-60348-0

Oligomers of pneumolysin form transmembrane channels in cholesterol-containing lipid bilayers. The mechanism of pore formation involves a multistage process in which the protein, at first, assembles into a ring-shaped complex on the outer-bilayer leaflet. In a subsequent step, the complex inserts into the membrane. Contrary to most investigations of pore formation that have focussed on protein changes, we have deduced how the lipid-packing order is altered in different stages of the pore-forming mechanism. An optical tweezing apparatus was used, in combination with microfluidics, to isolate large-unilamellar vesicles and control exposure of the bilayer to pneumolysin. By monitoring Raman-scattered light from a single-trapped liposome, the effect of the protein on short-range order and rotational diffusion of lipids could be inferred from changes in the envelope of the C–H stretch. A significant change in the lipid-packing order takes place during assembly of pre-pore oligomers. We were not able to detect a change in the lipid-packing order during the initial stage of protein binding, or any further change during the insertion of oligomers. Pre-pore complexes induce a transformation in which a bilayer, resembling a liquid-ordered phase is changed into a bilayer resembling a fluid-liquid-disordered phase surrounding ordered microdomains enriched in cholesterol and protein complexes.