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Suzuki Y. Influence of physico-chemical properties of chitin and chitosan on complement activation. Carbohydr Polym 2000. [DOI: 10.1016/s0144-8617(99)00161-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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2
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Nagar B, Jones RG, Diefenbach RJ, Isenman DE, Rini JM. X-ray crystal structure of C3d: a C3 fragment and ligand for complement receptor 2. Science 1998; 280:1277-81. [PMID: 9596584 DOI: 10.1126/science.280.5367.1277] [Citation(s) in RCA: 146] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Activation and covalent attachment of complement component C3 to pathogens is the key step in complement-mediated host defense. Additionally, the antigen-bound C3d fragment interacts with complement receptor 2 (CR2; also known as CD21) on B cells and thereby contributes to the initiation of an acquired humoral response. The x-ray crystal structure of human C3d solved at 2.0 angstroms resolution reveals an alpha-alpha barrel with the residues responsible for thioester formation and covalent attachment at one end and an acidic pocket at the other. The structure supports a model whereby the transition of native C3 to its functionally active state involves the disruption of a complementary domain interface and provides insight into the basis for the interaction between C3d and CR2.
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Affiliation(s)
- B Nagar
- Department of Biochemistry and Department of Molecular and Medical Genetics, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
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3
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Law SK, Dodds AW. The internal thioester and the covalent binding properties of the complement proteins C3 and C4. Protein Sci 1997; 6:263-74. [PMID: 9041627 PMCID: PMC2143658 DOI: 10.1002/pro.5560060201] [Citation(s) in RCA: 248] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The covalent binding of complement components C3 and C4 is critical for their activities. This reaction is made possible by the presence of an internal thioester in the native protein. Upon activation, which involves a conformational change initiated by the cleavage of a single peptide bond, the thioester becomes available to react with molecules with nucleophilic groups. This description is probably sufficient to account for the binding of the C4A isotype of human C4 to amino nucleophiles. The binding of the C4B isotype, and most likely C3, to hydroxyl nucleophiles, however, involves a histidine residue, which attacks the thioester to form an intramolecular acyl-imidazole bond. The released thiolate anion then acts as a base to catalyze the binding of hydroxyl nucleophiles, including water, to the acyl function. This mechanism allows the complement proteins to bind to the hydroxyl groups of carbohydrates found on all biological surfaces, including the components of bacterial cell walls. In addition, the fast hydrolysis of the thioester provides a means to contain this very damaging reaction to the immediate proximity of the site of activation.
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Affiliation(s)
- S K Law
- Department of Biochemistry, University of Oxford, United Kingdom.
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4
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Onishi M, Shimura K, Seita Y, Yamashita S. Design of a new plasma separation membrane by graft copolymerization. Radiat Phys Chem Oxf Engl 1993 1995. [DOI: 10.1016/0969-806x(95)00016-q] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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5
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Sahu A, Kozel TR, Pangburn MK. Specificity of the thioester-containing reactive site of human C3 and its significance to complement activation. Biochem J 1994; 302 ( Pt 2):429-36. [PMID: 8092994 PMCID: PMC1137246 DOI: 10.1042/bj3020429] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The specificity of the thioester-containing site in three plasma proteins is regulated by elements of their protein structures other than the thioester bond itself. Human C4A and alpha 2-macroglobulin preferentially form amide linkages while human C3 primarily forms ester linkages with hydroxyl groups. We have examined the thioester in C3 and found evidence of strong preferences for certain carbohydrates, indications of selectivity for specific positions on those carbohydrates and a preference for terminal sugars in polysaccharides. A testable set of rules are derived from these findings which predict preferred attachment sites on polysaccharides. A computer model of the effect of different reactivities on activation of the alternative pathway of complement suggested that organisms might greatly alter their susceptibility to complement with small changes in carbohydrate structure. While a random selection of 20 biological particles showed no correlation between activation and C3b attachment efficiency, subsets of related organisms differing primarily in their surface polysaccharide exhibited stronger correlations. The strongest correlation occurred in a series of the yeasts (Cryptococcus neoformans) possessing capsular polysaccharides with one, two, three or four branching xylose sugars per repeating unit. These organisms exhibited capture efficiencies for metastable C3b from 12% (one-xylose strain) to 41% (four-xylose strain).
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Affiliation(s)
- A Sahu
- Department of Biochemistry, University of Texas Health Science Center, Tyler 75710
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6
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Sepp A, Dodds AW, Anderson MJ, Campbell RD, Willis AC, Law SK. Covalent binding properties of the human complement protein C4 and hydrolysis rate of the internal thioester upon activation. Protein Sci 1993; 2:706-16. [PMID: 8495193 PMCID: PMC2142499 DOI: 10.1002/pro.5560020502] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The complement proteins C3 and C4 have an internal thioester. Upon activation on the surface of a target cell, the thioester becomes exposed and reactive to surface-bound amino and hydroxyl groups, thus allowing covalent deposition of C3 and C4 on these targets. The two human C4 isotypes, C4A and C4B, which differ by only four amino acids, have different binding specificities. C4A binds more efficiently than C4B to amino groups, and C4B is more effective than C4A in binding to hydroxyl groups. By site-directed mutagenesis, the four residues in a cDNA clone of C4B were modified. The variants were expressed and their binding properties studied. Variants with a histidine residue at position 1106 showed C4B-like binding properties, and those with aspartic acid, alanine, or asparagine at the same position were C4A-like. These results suggest that the histidine is important in catalyzing the reaction of the thioester with water and other hydroxyl group-containing compounds. When substituted with other amino acids, this reaction is not catalyzed and the thioester becomes apparently more reactive with amino groups. This interpretation also predicts that the stability of the thioester in C4A and C4B, upon activation, will be different. We measured the time course of activation and binding of glycine to C4A and C4B. The lag in the binding curve behind the activation curve for C4A is significantly greater than that for C4B. The hydrolysis rates (k0) of the thioester in the activated proteins were estimated to be 0.068 s-1 (t1/2 of 10.3 s) for C4A and 1.08 s-1 (t1/2 of 0.64 s) for C4B. These results indicate that the difference in hydrolysis rate of the thioester accounts, at least in part, for the difference in the binding properties of C4A and C4B.
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Affiliation(s)
- A Sepp
- Department of Biochemistry, University of Oxford, United Kingdom
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7
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Abstract
Purified C3 binds covalently to Jurkat T cells upon incubation at neutral pH. This binding does not appear to involve proteolysis of C3; it leads to high-molecular-weight associations, preferentially through ester linkages, which are disrupted upon incubation with hydroxylamine at alkaline pH. Part of the association also appears to involve disulfide links between C3 and Jurkat cells. Similarly, plasma membranes purified from these cells bind C3 with no evidence for proteolysis of C3. Binding of C3 appears to be "catalysed" by Jurkat cells, and is not due to the well-known spontaneous hydrolysis of C3. Binding of C3 involves hydrolysis of its thioester bond, as titratable--SH groups are available in soluble C3 after incubation of purified C3 with Jurkat plasma membranes; loss of C3 haemolytic activity confirms this finding. These observations give evidence for the binding of C3b-like C3 to Jurkat cells, conferring on these cells the potential to interact with other complement receptor-bearing cells such as B cells.
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Affiliation(s)
- C D Barro
- DBMS/ICH, Laboratoire d'Immunochimie, INSERM U238, Grenoble, France
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Affiliation(s)
- R P Levine
- James S. McDonnell Department of Genetics, Washington University School of Medicine, St. Louis, Missouri
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Kishore N, Shah D, Skanes VM, Levine RP. The fluid-phase binding of human C4 and its genetic variants, C4A3 and C4B1, to immunoglobulins. Mol Immunol 1988; 25:811-9. [PMID: 3264881 DOI: 10.1016/0161-5890(88)90117-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Covalent binding of the fourth complement protein, C4, to immune complexes is an important first step in the complement mediated processing of the complexes. Many of the initial encounters between the proteins of the complement system and antigen and antibody occur in solution, and prior to this report, studies of the interactions between them have focused on complement binding to preformed immune precipitates that most likely are not found in vivo. We have characterized the covalent binding of C4b to immunoglobulin molecules in a fluid-phase system consisting only of antibody in solution and purified C4 and C1s. We demonstrate that human C4b binds to IgG in the fluid phase, that its covalent binding is predominantly to the heavy chain of IgG, and that the covalent linkage is by either amide or acyl ester bonds. In addition, we compare the covalent binding efficiencies of two genetic variants of C4, C4A3 and C4B1, to IgG. C4A3 binds 3-4 times more IgG than C4B1 over a range of C4 concentrations, and C4A3 has a higher binding efficiency than C4B1 for IgM, IgA, IgG2a and F(ab')2 as well as for a protein antigen, BSA. Furthermore, we found that whereas C4A3 is bound to immunoglobulins in the fluid-phase predominantly by amide linkage, C4B1 is bound by either amide or acyl ester bonds. The results presented here suggest that the covalent binding efficiency of C4A3 and C4B1 to IgG is similar to that reported for their covalent binding to small molecules.
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Affiliation(s)
- N Kishore
- James S. McDonnell Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110
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10
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Abstract
The acyl ester bond between the third complement protein, C3, and a variety of molecules is hydrolyzed spontaneously at neutral pH (Venkatesh et al., 1984). Modification of the free, single sulfhydryl group of bound C3 by thiol reagents suggested that a functional group other than the -SH acts as a "catalytic" group in this intramolecular hydrolytic reaction. Complete inhibition of the esterase-like activity is observed with stoichiometric amounts of mercuric chloride, palladium chloride, and the bifunctional organic mercurial, 3,6-bis-(acetoxymercuri)-o-toluidine [BAMT]. Since alkyl and aryl mercuric ions do not inhibit the esterase-like activity of C3-[3H]glycerol, it is conjectured that divalent mercury, palladium, and BAMT will form a complex with the -SH group and an atom of the "catalytic" group X having a lone pair of electrons. The structural features of C3 that are essential for the esterase-like activity remain intact after subjecting C3-[3H]glycerol to covalent chromatography on organomercurial agarose. Based on the observed effects of chemical reagents and the kinetic deuterium solvent isotope effect on the esterase-like activity, a general-base mechanism is proposed for the intramolecular hydrolysis of the acyl ester bond in covalently bound C3. The "catalytic" group X is located in the C3d region (residues 317-632 of the alpha chain), since C3d-[3H]glycerol also has esterase-like activity. A general-base mechanism mediated by the same "catalytic" group X may also apply to the formation of acyl ester bonds following the hydrolysis of the internal thiolester bond in native C3.
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Affiliation(s)
- Y P Venkatesh
- Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110
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11
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Pryzdial EL, Isenman DE. A thermodynamic study of the interaction between human complement components C3b or C3(H2O) and factor B in solution. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)77937-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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12
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Alternative complement pathway activation fragment Ba binds to C3b. Evidence that formation of the factor B-C3b complex involves two discrete points of contact. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(19)75665-8] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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13
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The Esterase-Like Activity of Covalently Bound C3. Proteins 1987. [DOI: 10.1007/978-1-4613-1787-6_70] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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14
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Nilsson B, Nilsson UR. SDS denaturation of complement factor C3 as a model for allosteric modifications occurring during C3b binding: demonstration of a profound conformational change by means of circular dichroism and quantitative immunoprecipitation. Immunol Lett 1986; 13:11-4. [PMID: 2428739 DOI: 10.1016/0165-2478(86)90118-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The antigenic expression of bound but not fluid-phase C3b closely resembles that of sodium dodecyl sulphate (SDS) denatured C3. For this reason, denatured C3 has been used in this study as a model to characterize the conformational changes associated with bound C3b. It was shown in circular dichroism in the far UV spectrum that profound changes in the secondary structure occurred in denatured C3. Furthermore, quantitation by immunoprecipitation of the previously observed antigenic changes during denaturation demonstrated that C3 lost 2/3 of the antigens associated with native C3 whereas 1/3 were stable. The lost antigens were completely replaced by antigens that are specific for denatured and bound C3. We postulate that the binding of C3b is accompanied by a profound conformational change distinctive of that observed in fluid-phase C3b.
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Law SK, Minich TM, Levine RP. Covalent binding efficiency of the third and fourth complement proteins in relation to pH, nucleophilicity, and availability of hydroxyl groups. Biochemistry 1984; 23:3267-72. [PMID: 6432041 DOI: 10.1021/bi00309a022] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The binding of [3H]glycerol and [3H]putrescine to C3 was studied in a fluid-phase system using trypsin as the C3 convertase. The binding of glycerol showed little variation in the pH range between 6.0 and 10.0. The binding of putrescine (pKa = 9.0) is rather ineffective below pH 7.5 but becomes more efficient as the pH of the reaction mixture increases. These results agree with the contention that the final step of the binding reaction is the transfer of the acyl group of the exposed thio ester of C3 to a nucleophile since the nucleophilicity of hydroxyl groups is rather independent of pH whereas only the unprotonated form of amino groups is nucleophilic. The inefficient reaction of amino groups with the exposed thio ester of C3 is also supported by the study of the inhibitory activity of serine and its two derivatives, N-acetylserine and O-methylserine, to the binding of [3H]glycerol to C3. N-Acetylserine showed an inhibitory activity equivalent to that of serine, whereas O-methylated serine showed only minimal activity. It can be concluded, therefore, that serine reacts with the thio ester of C3 by its hydroxyl group but not by its alpha-amino group. The ability of the alcohol group of various alkanes to inhibit the binding of [3H]glycerol to C3 was also studied. The primary alcohols inhibit the binding reaction with an efficiency that is similar to glycerol, and there are no significant differences in the binding efficiencies of methanol, ethanol, 1-propanol, and 1-butanol.(ABSTRACT TRUNCATED AT 250 WORDS)
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Sim RB, Sim E. Autolytic fragmentation of complement components C3 and C4 and its relationship to covalent binding activity. Ann N Y Acad Sci 1983; 421:259-76. [PMID: 6202197 DOI: 10.1111/j.1749-6632.1983.tb18114.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The autolytic cleavage reaction of C3 and C4 and the covalent binding reaction of these proteins, are both aspects of the reactivity of an activated thiolester within these proteins. Autolytic cleavage occurs by internal nucleophilic attack on one face of the planar thiolester, while the covalent binding reaction of the activated proteins follows exposure of the opposite face of the thiolester to attack by external nucleophiles. Although the autolytic cleavage reaction does not occur under physiological conditions, the study of this phenomenon has provided valuable evidence in support of the mechanisms postulated for the physiological covalent binding reactions. The ease with which autolysis can be induced and observed in C3, C4, and alpha 2 M has provided a valuable method for detecting the active forms of these proteins in circumstances where other assays are impracticable, as, for example, in the examination of the uptake of active C3 by lymphocytes. Autolytic cleavage has also been used by Karp and colleagues to produce fragments used in characterizing genetic and biosynthetic variants of mouse C4 and the mouse protein Slp, which is structurally similar to C4. Gross structural comparisons made among C3, C4, and alpha 2 M on the basis of alignment of the autolytic cleavage sites and the protease-activation sites in these proteins were useful in predicting how the alpha-, beta-, and gamma-chains of C4, or the alpha- and beta-chains of C3, were aligned in the single polypeptide chain pro-forms of these proteins. The beta-alpha-gamma alignment deduced for C4 was also found by Goldberger and Colten. Similar alignments of cleavage sites have been used as a basis for evolutionary comparisons of complement proteins and alpha 2 M from species other than man. Although autolytic cleavage has been described only for C3, C4, alpha 2 M, and Slp, it is likely that other proteins will be found that exhibit this phenomenon. A possible candidate is pregnancy-associated plasma protein A (PAPP-A) which resembles alpha 2 M in many respects. The autolytic cleavage reaction will serve as a useful indicator in the detection of other proteins that undergo covalent binding by the mechanism discussed above.
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Tack BF. The beta-Cys-gamma-Glu thiolester bond in human C3, C4, and alpha 2-macroglobulin. SPRINGER SEMINARS IN IMMUNOPATHOLOGY 1983; 6:259-82. [PMID: 6198737 DOI: 10.1007/bf02116276] [Citation(s) in RCA: 78] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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18
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