Transcript C4-binding protein (C4BP)

Complement
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Complement is a collective term used
to designate a group of plasma and cell
membrane proteins that play a key role
in the host defense process.
The material, which complemented the
effect of antibody, could be restored by
the addition of fresh non-antibodycontaining serum and is known to
consist of a number of different plasma
proteins which operate as an enzyme
cascade similar to the coagulation
system.
Introduction
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原名: Alexin (1985, termed by Bordet who is a Nobel Prize winner)
Bacteriolysis by immune serum required a heat-stable bacterial antibody and a
heat-sensitive complement
Serum factors which could augment the effects of antigen-antibody combination.
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更名: Complement (termed by Ehrlich who is a Nobel Prize winner),
the activity of blood serum that completes the action of antibody
to exhibit a variety of biological properties in normal serum.
to be synthesized by liver hepatocytes or by tissue marcophages, epithelial cells
of gastrointestinal tract, and blood monocytes
to consist of a group of serum proteins that are not immunoglobulins
本身均為酵素原須經水解酵素作用後才具活性, 多數為鑲嵌型結構。
not to increase in their concentrations after immunization
The function of activated complements
溶解作用(Lysis)：經一連串反應補體蛋白會
形成一厭水性複合物，致使外來細胞滲透
壓失去平衡，使細胞產生溶解。
 調理作用(Opsonization)：補體蛋白與外物形
成複合物(the coating of the foreign particle)，
phagocytes可藉表面受器與補體複合物結合
將外物吞食並活化免疫細胞。
 活化作用(Activation)及清理(Clearance)：經一
連串免疫活或反應，補體蛋白會形成
peptide fragments，這些peptide fragments於組
織局部發炎時進行vasodilatation、phagocytic
cells遷移(如chemotaxis)及清除細胞感染物等
過程均扮演重要角色。
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The multiple activities of the complement system :
Lysis, opsonization, activation and clearance
The Complement System (補體系統)
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Most of biological effects of complement activation
involve the activation or fixation of the third
complement (C3), a sequential activation process to
ultimately cause their biologic effects.
具有區分自己與非自己的機轉的能力，可由
下列兩種路徑達成C3的活化：
The classical complement pathway：Under normal
physiologic conditions, this pathway is initiated by
antigen-antibody complexes.
The alternative complement pathway：This pathway
does not require antigen-antibody complexes for
initiation.
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Complement activation steps take place on cell or
basement mambrance, then they will proceed the
membrance attack pathway with the production of
lytic lesions.
Overview of the complement activation
pathway
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to involve nine major protein
complements, named C1~C9, in an
orderly fashion.
Overall plan of complement activation
The classical complement pathway
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Initial stage of activation
involves C1, C2, C3, and C4.
The classical complement pathway
The classical complement pathway
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C1:
A macromolecular complex:
composed of C1q、2C1r、
及2C1s and held together by
calcium ions.
– C1r及C1s (85 kDa)為 serine protease之proenzymatic form.
– C1q為具有six flower heads的構型，可與抗體的Fc部位接合；且僅
與IgM、IgG1-3接合，因此並非所有抗體均可活化classical pathway。
– 經由C1q與抗體的Fc部位接合，促使C1r活化後再活化C1s，形成C1
esterase，此酵素可協助C4a及C4b之形成。
Structure of C1q (a, b), C1r2s2 (c, d) and C1 complex (e)
The classical complement pathway
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C4 and C2:
C4具有3-polypeptide chain (α、β、γ)，經C1 esterase作用後行成C4a(small
fragment part)及C4b(large fragment part)。
C2具有1-polypeptide chain(102 kDa)。
C4b與C2結合(需Mg+2) 再經C1 esterase作用，釋放出C2b及形成C4b2a
complex(with enzymatic site，即為C3 convertase, 37℃半衰期為5分鐘)，此
complex可協助C3a及C3b之形成。
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C3:
C3為glycoprotein(1.2mg/ml of plasma)，具2-disulfide-linked chain (αandβchains
are 110 kDa and 75 kDa)。
經過C3 convertase作用後產生C3a及C3b。
C3a stimulates inflammation by causing degranulation of basophils and mast cells
and is chemotactic for neutrophil polymorphs, 因此C3a被稱為anaphylatoxin。
The classical complement pathway
C3b與C3 convertase (C4b2a3b, classical pathway C5 convertase)結合，形成
C5-9 complex固定於外來細胞表面，進行membrance attack pathway。
C3b會與Factor I及Factor H結合，形成iC3b(C3b is inactivated)。
C3b and iC3b mediate the phenomenon of immune adherence by their ability to
bind to C3 receptors on phagocytes.
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除與抗體接合引發classical pathway外，如mannan-binding protein、
C-reactive protein、lipid A of bacterial endotoxins、polyanions (such
as heparin)、polycations、denature DNA或virus membranes也可以
直接引發classical pathway，此種作用稱為nonimmunologic
classical pathway。
Schematic diagram of intermediates in classical pathway
The alternative complement pathway
The alternative complement pathway
The alternative complement pathway
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To be activated by C3(H2O) (low-level or tick-over C3)，即血清中只
要有少量的C3就能產生持續性的活化作用。
C3(H2O)經水解、蛋白酵素或C3 convertase(C3bBbP complex)作用
後產生C3a及C3b。
C3b、Factor B and Factor D
Factor B is a circulating protein and is similar in many respects to C2。
Factor D is a blood protein and is a C1-like serine protease
C3b及Factor B反應後，Factor D截切於Factor B上，釋出Ba fragment及
C3bBb complex。
C3bBb complex稱為alternative pathway C3 convertase，穩定性差，經過與
血液中之properdin (P)結合後，生成較穩定之convertase form (C3bBbP)，
C3bBbP的作用與classical pathway的C4b2a complex具有相同的作用。
C3b與C3 convertase (C3bBbC3b, alternative pathway C5 convertase)結合，形
成C5-9 complex固定於外來細胞表面，進行membrance attack pathway。
The lectin pathway
New complement pathway
 Lectina are proteins that bind to a carbohydrate
 Not to depend on antibody for its activation
 The mechanism is more like that of the classical pathway
 To be activated by mannose-binding lectin (MBL, an acute phase
protein produced in inflammatory respones) to mannose residues on
glycoprotein or carbohydrates on the surface of microbes
 Details of the lectin pathway remain obscure, but this means of
activating the C2-C4 componebts to form a C5 convertase without
need for specific antibody binding
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The membrane attack pathway
The last phase of the complement cascade.
 C5、C6、C7、C8 and C9
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受到C3b及C3 convertases (C4b2a or C3bBbC3b)作用，水解
成C5a and C5b；C5b生成後需立刻與C6結合(C5b6)穩定下
來，否則很容易就失去活性。
C5b6繼續與C7接合形成C5b67
complex附著於外來細胞表面上。
C5b67 complex is strongly
hydrophobic and is capable of
inserting into the lipid bilayer of cell
membranes.
The membrane attack pathway
C5b67 complex會陸續與一個C8
分子及多個C9分子(相互接合形
成筒狀，穿透鑲嵌於細胞膜上)
相結合，形成C5b678(9)n稱之為
membrane attack complex (MAC)。
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Membrane attack complex (MAC，
C5b678(9)n)
具有a hydrophobic outer surface,
which associates with the membrane
lipid of the bilayer。
具有a hydrophilic core, through
which small ions and water can pass。
The membrane attack pathway
The regulation of complement system
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The C1 inhibitor (C1INH)：C1INH is a glycoprotein (105 kDa), which can recognize
activated C1r and C1s and destroy their activity。
C4-binding protein (C4BP)：使C4b2a分解(放出C2a，C4b分解為C4c and C4d)。
Factor I：(1) 協助C4-binding protein (C4BP)，加速C4b2a之分解；(2) 加速C3bBb
之分解；(3) 蛋白水解C3b and C3(H2O)變成不活化物質(iC3b)。
Factor H：協助Factor I加速
C3bBb之分解，並蛋白水解C3b
變成不活化物質(iC3b)。
S protein：與C5b67 complex接觸，
防止C5b67 complex與細胞膜接
觸影響細胞穿孔的作用。
CD59：抑制C5b678與C9組合，
影響cell lysis。
The function of activated complements
溶解作用(Lysis)：經一連串反應補體蛋白會
形成一厭水性複合物，致使外來細胞滲透
壓失去平衡，使細胞產生溶解。
 調理作用(Opsonization)：補體蛋白與外物形
成複合物(the coating of the foreign particle)，
phagocytes可藉表面受器與補體複合物結合
將外物吞食並活化免疫細胞。
 活化作用(Activation)及清理(Clearance)：經一
連串免疫活或反應，補體蛋白會形成
peptide fragments，這些peptide fragments於組
織局部發炎時進行vasodilatation、phagocytic
cells遷移(如chemotaxis)及清除細胞感染物等
過程均扮演重要角色。
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E. coli cells was killed by complement-
mediated lysis
The role of C3b and antibody in opsonization
The Complement Receptors (補體受器)
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Receptors for activated C1q
On neutrophils、monocytes、the majority of B cells、lymphocytes lacking both B
and T cell markers。
to increase phagocytosis by phagocytic cells and oxidative metabolism。
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Receptors to anaphylatoxins (such as C3a)
on mast cells and serveral other cell types
to release histamine and other vasoactive
compounds
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Receptors for C3
CR1：CD35，C3b的受器。
CR2：CD21，C3d的受器。
CR3：CD11b/18，iC3b的受器。
CR4：CD11c/18，C3dg的受器 。
The Complement Receptors (補體受器)
The genetic considerations of complements
Most of the gene encoding proteins of the complement pathways have
been cloned, and their amino acid sequences have been determined。
 Almost all of the variants of complement proteins show autosomal
codominant inheritance at a sigle locus。
 The genes for C4, C2, and factor B are located within the MHC locus on
the short arm of chromosome 6 in human, MHC class III genes。
 The genes for many regulatory
proteins are grouped as a
supergene family on
chromosome 1；this family is
now known to encode factor H、
C4-binding protein、decayaccelerating factor、CR1 and
CR2。
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