Lecture 5 - Antibody Structure, Function and Genetics Flashcards

1
Q

Two types of antibodies

A

Membrane-bound and secreted

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2
Q

Light chain weight

A

25 kDa

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3
Q

Heavy chain weight

A

50kDa

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4
Q

Length of Ig domain

A

90-110 amino acids

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5
Q

Are there disulphide links between light chains?

A

No

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6
Q

Which parts make up antigen-binding domains?

A

Vh and Vl

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7
Q

Reason for flexible hinge region of antibody

A

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

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8
Q

CH2 domain role

A

Complement binding domain

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9
Q

CH3 domain role

A

Fc receptor binding site

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10
Q
Structure of Ig domain
1)
2)
3)
4)
5)
A

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

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11
Q

Classifications of Ig domains

A

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

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12
Q

LIght chain constant region order of strands

A

DEBA - GFC

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13
Q

Heavy chain variable region order of strands

A

DEBA - GFCCC`

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14
Q

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

A

B - F

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15
Q

What is the Ig superfamily?

A

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

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16
Q

What can members of the Ig superfamily not be?

A

Cytosolic proteins

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17
Q

How are members of the Ig superfamily normally encoded?

A

As a single exon

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18
Q
Examples of members of the Ig superfamily
1)
2)
3)
4)
5)
6)
A

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

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19
Q

Ig superfamily proteins are normally found where?

A

Bound in cell membranes

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20
Q

Two main proteases used to digest Ig domain

A

Pepsin

Papain

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21
Q

Where does papain cut?

A

Above disulphide hinge

22
Q

Where does pepsin cut

A

Below disulphide hinge

23
Q

Effects of cutting Ig domain with papain

A

2 regions:

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

24
Q

Effects of cutting Ig domain with pepsin

A

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

25
Structure of antibody-binding site
6 loops: 3 from light chain 3 from heavy chain
26
Complementarity determining regions
3 loops of each chain that make up antibody-binding site
27
Another term for complementarity determining regions
Hypervariable loops
28
Location of hypervariable loops on V domain
At roughly 30 amino acids, 50 amino acids and 100 amino acids
29
Where are the hypervariable loops located in an antibody?
All exposed on the ends of a natively-folded protein
30
Ratio of kappa to lambda light chains in humans
~2 kappa:1 lambda
31
Are kappa and lambda light chains ever mixed in a single antibody?
No
32
Serum [IgG]
12g/L
33
Serum [IgA]
3g/L
34
Serum [IgM]
1.5g/L
35
Serum [IgD]
0.3g/L
36
Serum [IgE]
0.0005g/L
37
Why is serum [IgE] so low?
IgE is bound to the surfaces of cells, such as Mast cells | Therefore not present in the blood at high concentrations
38
Why is serum [IgD] so low?
Lacks molecular ability to be secreted. | Some IgD is present in the blood because it can be cleaved off the surfaces of cells
39
Function of IgD
Cell surface receptor
40
Number of IgM mu chains
10
41
Does membrane-bound IgM have a J chain?
No
42
IgG distribution
Serum and lymph
43
IgM distribution
Serum
44
IgA distribution
Serum and mucosal secretions
45
IgE distribution
Below epithelial surfaces
46
``` IgG features 1) 2) 3) 4) ```
1) Monomer 2) Major Ig in secondary response 3) Large, flexible hinge region 4) High affinity
47
``` IgM features 1) 2) 3) 4) ```
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
48
J chain
15kDa protein involved in Ig oligeromisation | Bound to IgM and IgA
49
Affinity
The strength of binding between two molecules at a single site
50
Avidity
Sum total of strength of binding between two molecules, where multiple binding-sites are involved
51
``` IgA features 1) 2) 3) 4) ```
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
52
``` IgE features 1) 2) 3) 4) ```
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