F. K. Saunders

Pneumolysin, a membrane-damaging toxin, is known to activate the classical complement pathway. We have shown that 1 microgram ml-1 of pneumolysin can activate complement, which is a much lower level than observed previously. We have identified two distinct regions of pneumolysin which show homology with a contiguous sequence within acute-phase proteins, including human C-reactive protein (CRP). Site-directed mutagenesis of the pneumolysin gene was used to change residues common to pneumolysin and CRP. Some of the modified toxins had a reduced ability both to activate complement and bind antibody. We suggest that the ability of pneumolysin to activate complement is related to its ability to bind the Fc portion of immunoglobulin G.

The role of the single cysteine residue in the activity of the thiol-activated toxin pneumolysin was investigated using oligonucleotide-mediated, site-directed mutagenesis. Three modified toxins in which the cysteine residue was changed to an alanine, a serine, or a glycine residue were purified to homogeneity and examined for activity. The Cys-428----Ala modified toxin was indistinguishable from the wild-type recombinant toxin in terms of hemolytic activity and lytic and inhibitory effects on human polymorphonuclear leukocytes (PMN), indicating that the cysteine residue is not essential for toxin activity. The Cys-428----Ser and Cys-429----Gly modified toxins had reduced activity on erythrocytes and polymorphonuclear leukocytes, being 6 and 20 times less active than the wild type, respectively. However, all the modified toxins formed oligomers in erythrocyte membranes to the same extent as the wild-type recombinant toxin. This suggests that the cysteine residue at position 428 is involved in neither the binding of toxin to membranes nor its insertion into the membrane, and also that the formation of oligomers is not by itself sufficient for toxin activity.

Conference Article| June 01 1989 Bacterial capsules and interactions with complement and phagocytes I. S. ROBERTS; I. S. ROBERTS * *To whom correspondence should be addressed Search for other works by this author on: This Site PubMed Google Scholar F. K. SAUNDERS; F. K. SAUNDERS 1Department of Microbiology, University of Leicester, Leicester LE1 9HN, U.K. Search for other works by this author on: This Site PubMed Google Scholar G. J. BOULNOIS G. J. BOULNOIS 1Department of Microbiology, University of Leicester, Leicester LE1 9HN, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1989) 17 (3): 462–464. https://doi.org/10.1042/bst0170462 Article history Received: December 19 1988 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation I. S. ROBERTS, F. K. SAUNDERS, G. J. BOULNOIS; Bacterial capsules and interactions with complement and phagocytes. Biochem Soc Trans 1 June 1989; 17 (3): 462–464. doi: https://doi.org/10.1042/bst0170462 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search Keywords: PMNL, polymorphonuclear leucocyte, LPS, lipopolysaccharide, Mab, monoclonal antibody This content is only available as a PDF. © 1989 Biochemical Society1989 Article PDF first page preview Close Modal You do not currently have access to this content.