英文血红蛋白和抗体.pptx

77-1Biochemistry77-2Hemoglobin and Immunoglobulins77-3Myoglobin(p49 fig 7-3)77-4Structure of Myoglobina single polypeptide chain of 153 amino acidsa single heme group in a hydrophobic pocket8 regions of -helix;no regions of -sheetmost polar side chains are on the surfacenonpolar side chains are folded to the interiortwo His side chains are in the interior,involved with interaction with the heme groupFe(II)of heme has 6 coordinates sites;4 interact with N atoms of heme,1 with N of a His side chain,and 1 with either an O2 molecule or an N of the second His side chain77-5Heme structure P49 Figure 7-4 77-6Hemoglobin77-7Oxygen Binding of Hba tetramer of two -chains(141 amino acids each)and two -chains(153 amino acids each);2 2each chain has 1 heme group;hemoglobin can bind up to 4 molecules of O2 binding is cooperative;when one O2 is bound,it becomes easier for the next O2 to bindthe function of hemoglobin is to transport oxygenthe structure of oxygenated Hb is different from that of unoxygenated HbH+,CO2,Cl-,and 2,3-bisphosphoglycerate(BPG)affect the ability of Hb to bind and transport oxygen77-8Oxygen Binding of HbP51 Fig7-8:O2 binding of hemoglobin and myoglobinCooperativity of Binding/ReleaseThe oxygenation state(filled or empty)of one site of the multisubunit hemoglobin can be communicated to another site,resulting in cooperative binding and release of oxygen.Allosteric binding 77-9Oxygen Binding of HbThe effect of pH on the oxygen-binding ability of Hb is called the Bohr effect Bohr effect (p53 fig7-16)as pH decreases(more acidic),oxygen is releasedCO2 promotes release of O2 from HbO277-10Oxygen Binding of HbFigure The Bohr effect 77-11Oxygen Binding of HbTable Summary of the Bohr effect77-12Hemoglobin(Hb)Hemoglobin in blood is bound to BPGinteraction is electrostatic,between negative charges on BPG(2,3-bisphosphoglycerate,p53 fig7-17 fig 7-19)and positive side chains(e.g.,Lys,Arg)of hemoglobinBPG promotes O2 dissociationHb stripped of BPG remains saturated with O277-13Fetal Hemoglobin,Hb Fhas a higher affinity for O2 than maternal Hb Astructure is 2g g2binds less strongly to BPG that does Hb AFigure:Oxygen binding capacity of Hb F 77-14Abnormal Human Hb(Hb Variants)Hb S:substitution of Val for Glu at 26 Hb E:Glu B8(26)-Lys;change is on the surface and has little effect on Hb stability or functionHb Savannah:Gly B6(24)-Val;not enough room for Val between B-helix and E-helix which disrupts entire structureHb Bibba:Leu H19(136)-Pro;proline disrupts the H-helixHb M Iwate:His F8(87)-Tyr;blood contains methemoglobin and blood is chocolate brownHb Milwaukee:Val E11(67)-Glu;glutamate side chain forms an ion pair with heme iron which stabilizes Fe(III)and prevents O2 binding77-15Fig 7-21 p5477-16Evolution of Myoglobin/Hemoglobin ProteinsOut of the 153 amino acids in the amino acid sequences of sperm whale myoglobin and human myoglobin,there are only 25 differences.(100 million years)Conserved Amino Acid Sequences-During the long evolution of the myoglobin/hemoglobin family of proteins,only a few amino acid residues have remained invariant.77-17ImmuglobulinsAntigens and Antibodies-The foreign substance that elicits an immune response is called the antigen.A specific immunoglobulin that binds to the antigen is called the antibody.1.Humoral immune response-Lymphatic cells called B lymphocytes synthesize specific immunoglobulin molecules that are excreted from the cell and bind to the invading substance.Binding either precipitates the foreign substance or marks it for destruction by cells called macrophages.2.Cellular immune response-Lymphatic cells called T lymphocytes,bearing immunoglobulin-like molecules on their surfaces,recognize and kill foreign or aberrant cells.77-18TermsAntigen:Foreign material that is recognized by the immune system,it is usually a protein,but it can be a peptide,or carbohydrate.Epitope:Region of a protein antigen to which the antibody binds.Hapten:A small chemical that is an antigen.77-19Antibody Structure:1 Quaternary structure(2 Light+2 Heavy chains).The two heavy and light chains are held together by non-covalent forces and covalent(disulfide)bonds.The light chain consists of two immunoglobulin folds and the heavy chain contains four of these domains:The overall shape is that of a Y.Two antigen binding sites/antibody.77-20Antibody structure2 Immunoglobulin fold is an example of a protein domain or a motif.It contains 7 -strands that form a two sheet sandwich with 4 stands on one side and 3 on the other.A buried disulfide bond crosslinks the two faces.77-21Antibody structure3 Disulfide bonds covalently join the heavy and light chains,conferring stability on this secreted protein(Some antibodies are secreted outside the body)4 hypervariable regions(CDR(Complementary determining region)The first immunoglobulin domain of the heavy and light chain contains three special segments of primary sequence that vary in their primary sequence from one antibody to the next.5 In the folded form of the antibody the three hypervariable regions of each chain come together in space to form the binding site for foreign material.CDRCDR77-22Antibody structureFab fragments can be further reduced to Fv fragments,consisting of the 1st immunoglobulin fold from the heavy and light chain.The Fv domain is the smallest unit that can bind antigen.FabFabFcFc77-23Practical Uses of Immunoglobulins:a.Fluorescence tagging(to label various components in the cell)b.Purification of materials(More on this later)c.Immunotherapy(see Campbell)d.Novel chemical reactions(Some antibodies can actually perform chemical reactions)e.Drug detoxification,see Chime page on Antibodies and Angel dust(PCP)