Structure and Function of

Antibodies

Folder Title: Antibody

Updated: October 01, 2013

See parts of Chapter 3, Kuby Edition 7; B and T-Cell ReceptorsAntibody Structure: pages 80 – 94Display of Current Cover: Science ANTIBODIES

Targets and Weapons in the Specific Adaptive Immune Response

Responds to Antigenic Determinants (Epitopes)

Responds With:

Lymphocyte Receptor Primary "Weapon"

B-Cell Membrane-bound Antibody Extra-cellular Antibody

T-Cell T-Cell Receptor Extra-cellular Cytokines

Fab Region

Fc Region

“Fc” = FragmentCrystallizable”“Fab” = FragmentAntibody Binding(not crystallizable)

Protein Structure of Antibodies

A dimeric protein

Heavy and Light Chains

2 Heavy – 2 Light

One Set or Multiple Sets depending on the antibody isotype and antibody role

Antibodies as Serum Proteins:

Which serum proteins are they?

What do they look like?

See Box 3-1, Figure 1Kuby 7th Edition

Adding Soluble Antigen to Blood SerumWhich protein fraction decreased?

Where did it go?

Antigen Added

Untreated BloodSerum

Tetrameric

Structure

of IgG

Figure 5-2, Kuby 3rd Ed.

IgG4mer

See Figure 4-7Kuby, 6th Editionp. 86

Complementarity of

Antibody – Antigen Binding

As Proteins: How Do Antibodies Bind to Virtually an

Infinite Number of Different Possible Antigens?

Representation of Sequence Comparisons Among Light Chains from Antibodies with Three Different Antigen Specificities

H3N-Ser-Val-Ile-Thr-Gly-Gly-Tyr-Ala... Thr-Glu-Ala-Val-Tyr-Ser-Met-COO-

H3N-Ser-Ile-Met-Thr-Arg-Leu-Tyr-Gly..Thr-Glu-Ala-Val-Tyr-Ser-Met-COO-

H3N-Thr-Gly-Gly-Thr-Lys-Leu-Tyr-Ile..Thr-Glu-Ala-Val-Tyr-Ser-Met-COO-

Variable Amino Terminal Half Conserved Carboxyl Terminal Half

(Positions 1 to 107) (Positions 108 - 214)

Complementarity-determining Regions (CDR’s) from Light and Heavy Chains Come together in 3 dimensions to give the antigen-recognizing site.

Following are three Turning Point short answer questions.

Please put all notes on the floor.Do not have any electronic devices other than your NXT transmitter.No consulting with other students.

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If you have a problem using your NXT device, please ask Elisabeth for help.

It is imperative that the integrity of these in-class Turning Point quizzes be maintained at the same level as we will do with the three written exams.

The red curve shows the separation of blood serum proteins into four peaks (Albumins, alpha, beta, and gamma globulin fractions). The black curve

shows what happens when an antigen to which the patient has been sensitized is added to the blood serum. What does

this tell us?

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Antibody structure is divided in V-regions and C-regions.What do “V” and “C” stand for?

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What does the “V” region of antibodies do in chemical or immunological terms?

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What Produces Antibody – Antigen Specificity?

Why Do We get Specificity and Very Tight Affinity?

Figure 9.13 The Biology of Cancer (© Garland Science 2007)

Yellow is p53 protein showing peptide domain sequence that binds to MDM2 Control Protein

Blue shows topology of pocket in MDM2 protein that binds to p53

How proteins recognize each other topologically (3-dimensional surfaces)

Large surface protein epitope recognized

Smaller low molecular size epitopes recognized

Small peptide antigen binding to an Fab (Fragment-antibody-binding) fragment of a complementary antibody

Conformational change in antibody upon binding antigen (“induced fit”)

Peptide antigen from an HIV protein antigen

Light and heavy chain CDR regions move to better complement the antigen

Movement of Peptide-binding Pocket

Accompanying Antigen Binding:

Fab Fragment of Antibody to Hemagglutinin Peptide

Figure 5-11

Kuby, 3rd EdAgAbMove

How does the antibody protein

recognize its complementary

antigen so precisely?

Precise topological, spatial, and directional arrangement of stabilizing bonding.

Minimization of repulsive interactions.

Immunoglobulin Isotypes

Structures and Functions

See Figure 4-6,Kuby 6th Editionp. 85

See Figure 4-6,Kuby 6th Editionp. 85

Heavy ChainIso-forms

Variable RegionsIncluding hypervariable CDR’s (Complementarity determining regions)

κ or λ forms

The Heavy and light chains are labeled incorrectly in the Kuby Immunology Powerpoint slides. The figure is labeled correctly in the book.

Chain Structures of the five immunoglobulin classes in humans

(adapted from Kuby, 2nd edition)

Class Heavy Light Sub-Classes Subunit Formula

Chain Chain

IgG γ κ or λ γ1, γ2, γ3, γ4 γ2κ2 γ2λ2

IgA α κ or λ α1, α2 (α2κ2)n

(α2λ2)n

n =1,2,3,4

IgM μ κ or λ None (μ2κ2)n

~ (μ2λ2)n

~ n = 1 or 5

IgD δ κ or λ None δ2κ2 δ2λ2

IgE ε κ or λ None ε2κ2 ε2λ2

IgClass

IgAModl

Figure 5-17(a)

Kuby, 3rd Ed.

Structures of Four Sub-types of IgG

Figure 5-16, Kuby, 3rd Ed.IgGSubs

See Figure 4-18Kuby, 6th Editionp. 98

Properties & Activities of Human Serum Immunoglobulins (from Table 4-2, Kuby Immunology, 4th Ed. p. 96)

Property or Activity IgG* IgA** IgM IgE IgD#

Mol Wt (KD) 150 150 – 600 900 190 150H Chain gamma alpha mu epsilon deltaSerum Conc (mg/ml) 0.5 – 9 0.5 - 3 1.5 0.0003 0.03Serum Half-life (dys) 8 - 23 6 5 2.5 3Activate Complement Yes No Strong No

NoCross Placenta Yes No No No NoMembrane (mIg) Form No No Yes*** No YesFc Binds Macrophages Yes No ? No NoMucosal Presence No Strong Yes No NoInduces Mast Cell No No No Yes No* 4 Sub-classes IgG1, IgG2, IgG3, IgG4**2 Sub-classes IgA1, IgA2 (exists as mono-, di-, tri, tetramer)*** mIgM is monomer. Serum IgM is pentamer # Has no known effector function. Is a membrane-bound antigen receptor

Functions of Fab BindingNeutralization or Blocking of Target Molecule or ParticleCross-linking and Agglutination of Target (Bivalent Fab Binding)

Functions of Fc RegionComplement Fixation and Lysis of TargetOpsonization (Coating by Ab) and Phagocytosis of TargetTargeting by Antibody for Cell-mediated Destruction(Antibody-dependent Cell-mediated Cytotoxicity: ADCC)Mast Cell Attraction and Activation by Bound IgE

Immediate Type I Hypersensitivity, Type I Allergic Response, Localized and Systemic Anaphylaxsis

Effector Functions of Antibodies

Effector

Following are three Turning Point short answer questions.

Please put all notes on the floor.Do not have any electronic devices other than your NXT transmitter.No consulting with other students.

If you have a problem with your device, I can provide you with a loaner NXT device.

If you have a problem using your NXT device, please ask Elisabeth for help.

It is imperative that the integrity of these in-class Turning Point quizzes be maintained at the same level as we will do with the three written exams.

The amino terminal one-half of the light chains of antibodies, and the amino terminal one-fourth of the heavy chains are called the ___________ regions.

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The hypervariable regions in the variable regions of the antibody heavy and light chains actually are responsible for antigen recognition

and binding. These hypervariable regions are called ____ ____ ____ ‘s

(if you don’t exactly remember the 3-letter abbreviation you can spell out part of the first word defining these regions)

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Give an example of an immunoglobulin isotype using the abbreviations commonly employed to define isotypes

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Antibodies as Antigens

Why does this matters?

If we want to use antibodies as therapeutic agents in patients, we have to understand and control the immunogenicity of the antibodies, or they will generate damaging and dangerous allergic responses,and be cleared from the patient and would be ineffective at best.

Antibodies are not cells, so they don’t have transplantation antigens and they don’t have to be histocompatibility matched, but they have to go unrecognized as foreign proteins and they cannot be allowed to generate allergic reactions in the recipient.

Antibodies as Antigens

1.Different Heavy Chain Isotypes (gamma, alpha, mu, epsilon, delta): Anti-isotype Antibodies (Anti-gamma, Anti-Alpha, Anti-Mu, etc)

(Also differences in constant regions of kappa and lambda light chains)

2. Different individual mouse strains (or different people):Anti-allotype Antibodies (Antibodies from one person would raise

anti-antibodies in a non-identical twin recipient)

(1 and 2: Like any other proteins with multiple molecular forms)

3. Different antigen-recognition abilities: Anti-idiotype Antibodies. Anti-CDR’s for different antibodies

Other proteins except for T-cell Receptors do not show these kinds of variations and are not immunogenic in this way

Transplantation Concepts and Nomenclature

From self, from identical twin, or from and to inbred animals of the same strain:

Syngeneic, Isogeneic, Isologous

From same species but not self or identical twin:Allogeneic

(“allo” = other)

From different species (e.g mouse to human)Xenogeneic

(“Xeno” = foreign)

Isoforms of the same antibody in the same individual

Allotypic determinants (different individuals) are in the Constant Regions of Heavy and Light Chains

Idiotypic determinants are in the V-regions of Heavy and Light Chains , especially at the CDR’s)

Therapeutic Monoclonal antibody would use antibody matched as isotype and matched in the framework allotype (i.e matched as close as possible to the patient).

Then graft in the CDR’s from mouse to get the antigenic specificity that is needed. Foreign idiotopes could go unrecognized and be non-immunogenic.

Matched human isotype and human allotype.Graft in mouse CDR’s

Humanized monoclonal Ab

Following are two Turning Point short answer questions.

Please put all notes on the floor.Do not have any electronic devices other than your NXT transmitter.No consulting with other students.

If you have a problem with your device, I can provide you with a loaner NXT device.

If you have a problem using your NXT device, please ask Elisabeth for help.

It is imperative that the integrity of these in-class Turning Point quizzes be maintained at the same level as we will do with the three written exams.

What is the advantage of using a “humanized” monoclonal antibody in therapy in patients?

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Anti-idiotype (idiotope) antibodies are directed to what part of the therapeutic antibody that is the immunogic and

is under attack?

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View from OnLine at Textbook Web-site:

Molecular Animation of Immunoglobulin Structure

Molecular Animation of Cells of the Immune Response

Molecular Visualization of Immunoglobulin Structure

Molecular Visualization of Antigen-Epitope Interactions

For OnLine Access to Immunology Edition 6 Information:

http://bcs.whfreeman.com/immunology6e

Avastin for Breast Cancer: Possible withdrawal of FDA approval. Sept. 16, 2010

 http://www.cnn.com/video/#/video/health/2010/09/17/dnt.cohen.breast.cancer.cnn?iref=allsearch

View Cancer Warrior, NOVA OnLine Video, 2001http://www.pbs.org/wgbh/nova/body/cancer-warrior.html

Judah Folkman, Endostatin, Angiostatin, and Targeting Cancer Vascularization

“Judah will cure cancer in three years” (J. D., Watson, 2001)

Anti-angiogenesis factor receptor monoclonal antibody: Avastin

This question and the next one are anonymous. They will not be graded and your name will not be recorded by the system.

What language to you understand the best?

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This is also anonymous. It will not be graded and your name will not be recorded by the system. We are trying to determine the best way to

present Immunology in class and the best way to give and to grade the quizzes and exams.

With respect to English as spoken in class , as shown on the screen, and as used in the quizzes

A. I am comfortable with English and I can follow and respond with no language problem.

B. I have some difficulty with English, but I can follow in class and respond to the quizzes most of the time.

C. I have a lot difficulty following what you are saying in class and in sending in responses to the quiz questions.

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