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

Which parts make up antigen-binding domains?

Answer 6

Vh and Vl

Question 7

Reason for flexible hinge region of antibody

Answer 7

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

Question 8

CH2 domain role

Answer 8

Complement binding domain

Question 9

CH3 domain role

Answer 9

Fc receptor binding site

Question 10

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

Answer 10

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 11

Classifications of Ig domains

Answer 11

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

Question 12

LIght chain constant region order of strands

Answer 12

DEBA - GFC

Question 13

Heavy chain variable region order of strands

Answer 13

DEBA - GFCCC`

Question 14

Which strands in a light chain B-pleated sheet join with a disulphide bridge?

Answer 14

B - F

Question 15

What is the Ig superfamily?

Answer 15

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

Question 16

What can members of the Ig superfamily not be?

Answer 16

Cytosolic proteins

Question 17

How are members of the Ig superfamily normally encoded?

Answer 17

As a single exon

Question 18

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

Answer 18

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

Question 19

Ig superfamily proteins are normally found where?

Answer 19

Bound in cell membranes

Question 20

Two main proteases used to digest Ig domain

Answer 20

Pepsin

Papain

Question 21

Where does papain cut?

Answer 21

Above disulphide hinge

Question 22

Where does pepsin cut

Answer 22

Below disulphide hinge

Question 23

Effects of cutting Ig domain with papain

Answer 23

2 regions:

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

Question 24

Effects of cutting Ig domain with pepsin

Answer 24

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

Question 25

Structure of antibody-binding site

Answer 25

6 loops:
3 from light chain
3 from heavy chain

Question 26

Complementarity determining regions

Answer 26

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

Question 27

Another term for complementarity determining regions

Answer 27

Hypervariable loops

Question 28

Location of hypervariable loops on V domain

Answer 28

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

Question 29

Where are the hypervariable loops located in an antibody?

Answer 29

All exposed on the ends of a natively-folded protein

Question 30

Ratio of kappa to lambda light chains in humans

Answer 30

~2 kappa:1 lambda

Question 31

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

Answer 31

No

Question 32

Serum [IgG]

Answer 32

12g/L

Question 33

Serum [IgA]

Answer 33

3g/L

Question 34

Serum [IgM]

Answer 34

1.5g/L

Question 35

Serum [IgD]

Answer 35

0.3g/L

Question 36

Serum [IgE]

Answer 36

0.0005g/L

Question 37

Why is serum [IgE] so low?

Answer 37

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

Therefore not present in the blood at high concentrations

Question 38

Why is serum [IgD] so low?

Answer 38

Lacks molecular ability to be secreted.

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

Question 39

Function of IgD

Answer 39

Cell surface receptor

Question 40

Number of IgM mu chains

Answer 40

10

Question 41

Does membrane-bound IgM have a J chain?

Answer 41

No

Question 42

IgG distribution

Answer 42

Serum and lymph

Question 43

IgM distribution

Answer 43

Serum

Question 44

IgA distribution

Answer 44

Serum and mucosal secretions

Question 45

IgE distribution

Answer 45

Below epithelial surfaces

Question 46

IgG features
1)
2)
3)
4)

Answer 46

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

Question 47

IgM features
1)
2)
3)
4)

Answer 47

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 48

J chain

Answer 48

15kDa protein involved in Ig oligeromisation

Bound to IgM and IgA

Question 49

Affinity

Answer 49

The strength of binding between two molecules at a single site

Question 50

Avidity

Answer 50

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

Question 51

IgA features
1)
2)
3)
4)

Answer 51

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 52

IgE features
1)
2)
3)
4)

Answer 52

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