Lecture 5 - Antibody Structure, Function and Genetics

Question 1

Two types of antibodies

Answer 1

Membrane-bound and secreted

Question 2

Light chain weight

Answer 2

25 kDa

Question 3

Heavy chain weight

Answer 3

50kDa

Question 4

Length of Ig domain

Answer 4

90-110 amino acids

Question 5

Are there disulphide links between light chains?

Answer 5

No

Question 6

Reason for flexible hinge region of antibody

Answer 6

Makes it less necessary for antigen to be placed very precisely relative to antibody binding site

Question 7

CH2 domain role

Answer 7

Complement binding domain

Question 8

CH3 domain role

Answer 8

Fc receptor binding site

Question 9

Structure of Ig domain
1)
2)
3)
4)
5)

Answer 9

1) 90 - 100 amino acids long
2) 2 layers of beta-pleated sheet
3) between 3 - 5 antiparallel strands
4) Hydrophobic residues point inwards to form a hydrophobic core
5) Conserved cysteine regions form disulphide bridge

Question 10

Classifications of Ig domains

Answer 10

V-like of C-like, depending on similarity to variable or constant regions

Question 11

What is the Ig superfamily?

Answer 11

Proteins that share structural and amino-acid homology with light or heavy chains

Question 12

What can members of the Ig superfamily not be?

Answer 12

Cytosolic proteins

Question 13

How are members of the Ig superfamily normally encoded?

Answer 13

As a single exon

Question 14

Examples of members of the Ig superfamily
1)
2)
3)
4)
5)
6)

Answer 14

1) TCR
2) MHCI
3) MHC II
4) IgG
5) Cd4
6) CD8

Question 15

Ig superfamily proteins are normally found where?

Answer 15

Bound in cell membranes

Question 16

Two main proteases used to digest Ig domain

Answer 16

Pepsin

Papain

Question 17

Where does papain cut?

Answer 17

Above disulphide hinge

Question 18

Where does pepsin cut

Answer 18

Below disulphide hinge

Question 19

Effects of cutting Ig domain with papain

Answer 19

2 regions:

1) Fab (can bind antigens)
2) Fc (can be crystallised)

Question 20

Effects of cutting Ig domain with pepsin

Answer 20

1 large region:
Fab`2 - Can bind antigen, is dimeric
Other region degrades

Question 21

Structure of antibody-binding site

Answer 21

6 loops:
3 from light chain
3 from heavy chain

Question 22

Complementarity determining regions

Answer 22

3 loops of each chain that make up antibody-binding site

Question 23

Another term for complementarity determining regions

Answer 23

Hypervariable loops

Question 24

Location of hypervariable loops on V domain

Answer 24

At roughly 30 amino acids, 50 amino acids and 100 amino acids

Question 25

Where are the hypervariable loops located in an antibody?

Answer 25

All exposed on the ends of a natively-folded protein

Question 26

Ratio of kappa to lambda light chains in humans

Answer 26

~2 kappa:1 lambda

Question 27

Are kappa and lambda light chains ever mixed in a single antibody?

Answer 27

No

Question 28

Serum [IgG]

Answer 28

12g/L

Question 29

Serum [IgA]

Answer 29

3g/L

Question 30

Serum [IgM]

Answer 30

1.5g/L

Question 31

Serum [IgD]

Answer 31

0.3g/L

Question 32

Serum [IgE]

Answer 32

0.0005g/L

Question 33

Why is serum [IgE] so low?

Answer 33

IgE is bound to the surfaces of cells, such as Mast cells

Therefore not present in the blood at high concentrations

Question 34

Why is serum [IgD] so low?

Answer 34

Lacks molecular ability to be secreted.

Some IgD is present in the blood because it can be cleaved off the surfaces of cells

Question 35

Function of IgD

Answer 35

Cell surface receptor

Question 36

Number of IgM mu chains

Answer 36

10

Question 37

Does membrane-bound IgM have a J chain?

Answer 37

No

Question 38

IgG distribution

Answer 38

Serum and lymph

Question 39

IgM distribution

Answer 39

Serum

Question 40

IgA distribution

Answer 40

Serum and mucosal secretions

Question 41

IgE distribution

Answer 41

Below epithelial surfaces

Question 42

IgG features
1)
2)
3)
4)

Answer 42

1) Monomer
2) Major Ig in secondary response
3) Large, flexible hinge region
4) High affinity

Question 43

IgM features
1)
2)
3)
4)

Answer 43

1) Pentamer
2) Has extra C domain (3 C domains, 3 of which make up Fc tail structure)
3) High avidity, low affinity
4) 26aa ‘tail piece’ linked to J chain

Question 44

J chain

Answer 44

15kDa protein involved in Ig oligeromisation

Bound to IgM and IgA

Question 45

Affinity

Answer 45

The strength of binding between two molecules at a single site

Question 46

Avidity

Answer 46

Sum total of strength of binding between two molecules, where multiple binding-sites are involved

Question 47

IgA features
1)
2)
3)
4)

Answer 47

1) Dimer (tetravalent)
2) Major Ig secreted in GIT and respiratory tracts
3) 26aa tailpiece bound to J chain
4) Uses secretory component to bind to pIgR to transcytose across luminal membrane into luminal space

Question 48

IgE features
1)
2)
3)
4)

Answer 48

1) Has extra Fc domain
2) Involved in allergic reactions and anti-parasitic immunity
3) Inflexible hinge region
4) Binds to mast cells, induces degranulation