Lysis

About: Lysis is a research topic. Over the lifetime, 6072 publications have been published within this topic receiving 216978 citations.

Streptococcal inhibitor of complement (SIC) inhibits the membrane attack complex by preventing uptake of C567 onto cell membranes

Abstract: Streptococcal inhibitor of complement (SIC) was first described in 1996 as a putative inhibitor of the membrane attack complex of complement (MAC). SIC is a 31 000 MW protein secreted in large quantities by the virulent Streptococcus pyogenes strains M1 and M57, and is encoded by a gene which is extremely variable. In order to study further the interactions of SIC with the MAC, we have made a recombinant form of SIC (rSIC) in Escherichia coli and purified native M1 SIC which was used to raise a polyclonal antibody. SIC prevented reactive lysis of guinea pig erythrocytes by the MAC at a stage prior to C5b67 complexes binding to cell membranes, presumably by blocking the transiently expressed membrane insertion site on C7. The ability of SIC and clusterin (another putative fluid phase complement inhibitor) to inhibit complement lysis was compared, and found to be equally efficient. In parallel, by enzyme-linked immunosorbent assay both SIC and rSIC bound strongly to C5b67 and C5b678 complexes and to a lesser extent C5b-9, but only weakly to individual complement components. The implications of these data for virulence of SIC-positive streptococci are discussed, in light of the fact that Gram-positive organisms are already protected against complement lysis by the presence of their peptidoglycan cell walls. We speculate that MAC inhibition may not be the sole function of SIC.

Components of guinea pig complement. i. separation of a serum fraction essential for immune hemolysis and immune adherence.

Abstract: Employing sheep erythrocytes sensitized by antibody and the first and fourth components of complement (EAC'1,4), in such a manner as to prevent the development of immune adherence (I-A) reactivity during preparation, four separate substances required for the conversion of EAC'1,4,2 to the final damaged state (E*) were identified in whole guinea pig serum by cellulose chromatography, and tentatively termed C'3c, C'3b, C'3a, and C'3d. I-A reactivity was induced in EAC'1,4,2 after interaction with only one of these four substances, C'3c. A detailed comparison of the effects of heat, hydrazine, low pH, freezing, absorption by immune complexes, and elution from cellulose columns indicated that this same substance which was capable of imparting I-A reactivity to EAC'1,4,2 was also essential for immune hemolysis. Other experiments showed that I-A-reactive cells prepared either by treating EA with different concentrations of whole C' at 0°C, or by treating EAC'1,4,2 with C'3c, underwent lysis by C'2 + C'3b + a + d in proportion to the amount of whole C' or of C'3c used to make the cells reactive in I-A. These data provide strong evidence that a single factor, C'3c, is required both for the conversion of EAC'1,4,2 to an I-A-reactive complex (EAC'1,4,2,3c) and for the lysis of EAC'1,4,2 by C'3b + a + d. C'3c is the only one of the components studied which can induce I-A reactivity, and is the first to react with EAC'1,4,2. Formation of EAC'1,4,2,3c proceeds even at 0°C, but is much more rapid at elevated temperatures, showing a maximum in from 5 to 15 minutes at 37° or 30°C respectively. Prolonged incubation at these temperatures results in a decline in hemolytic reactivity without a noticeable effect on I-A. This loss was resolved into three phenomena: (a) a rapid loss of ability of SAC'1,4,2,3c to react with C'3b, presumably as a result of decay of the C'2 moiety in the complex, which is readily reversed by addition of fresh C'2; (b) a slow, irreversible spontaneous inactivation of SAC'1,4,2,3c; (c) a moderately rapid, irreversible inactivation of SAC'1,4,2,3c by some factor present in C'3c preparations.

beta-Glucosidase excretion by Trichoderma pseudokoningii: correlation with cell wall bound beta-1.3-glucanase activities.

Abstract: The formation and excretion of beta-glucosidase from Trichoderma pseudokoningii was studied during growth on different carbon sources. The enzyme was present under all conditions examined, but increased activity was found during growth on carbon sources favouring slow growth. Two different patterns of beta-glucosidase excretion were observed: on carbon sources allowing fast growth a relatively high percentage of total activity was found in the culture fluid, which decreases as the culture grows older, but which increases again during the phase of cell lysis; on carbon sources favouring slow growth, excretion is initially low, but commences at later culture stages. Changes in cell wall composition and cell wall lytic enzyme activities associated with the cell walls were examined during phases of high and low ratios of extracellular to cell-wall bound beta-glucosidase activities. With no component of the cell wall (chitin, alpha-glucan, beta-glucan, galactosamine) could correlation with beta-glucosidase excretion be identified. Among a number of cell-wall lytic, cell-wall associated enzymes (alpha-glucanases, beta-glucanases, glucosaminidase, galactosaminidase), beta-1.3-glucanase activity correlated well with the excretion of beta-glucosidase. The results suggest a possible role of beta-1.3-glucanases in the mechanism of release of beta-glucosidase from cell walls of T. pseudokoningii; this is discussed.