Transcript No Slide Title

CLINICAL ASPECTS OF BIOCHEMISTRY
PROTEINS AND DISEASE
MIKE WALLIS
Structural/fibrous proteins
Lectures 2-3: Elastin, Resilin, Silk, Keratin
ELASTIN
• Connective tissue - especially ligaments, blood vessels, trachea and
bronchi. Very stretchy.
• Elastic fibres - not striated - fibrous and amorphous component
(amorphous component is elastin).
• Very insoluble; more soluble form extractable from Cu2+ deficient
animals - more Lys, less cross links. This is tropoelastin/proelastin.
• 700-800 aas in peptide chains.. Rich in non-polar aas (esp. Gly, Ala,
Val, Pro); no His, Cys, Met, Trp.
• Little recognisable secondary structure, though maybe 15-20% ahelix.
• ~33% Gly, ~20% Pro and some HydroxyPro and HydroxyLys.
Sequences from tropoelastin
-Pro-Gly-Val-Gly-Val-Pro-Gly-Val-Gly-ValPro-Gly-Val-Gly-Val-Pro-Gly-Val-Ser-ValPro-Gly-Val-Gly-Val-Pro-Gly-Val-Gly-Val-
and repeats of:
-Lys-Ala-Ala-Lys-Lys-Ala-Ala-Ala-Lys-
Tropoelastin
Elastin crosslinks - desmosine
Elastin cross link formation
Cu2+
Lysyl oxidase
Oiled-coil model for elastin
"oiled coil"
desmosine cross links
ELASTIN DEFECTS
Williams syndrome - growth defects, cardiovascular
problems, mental retardation..
Supravulvular aortic stenosis - cardiovascular
problems
Due to deletion of all or part of elastin gene, or (less
commonly) substitutional point mutations in elastin
gene
Elastin defects may also be associated with vascular
problems, ageing etc.
THE ELASTIN GENE
Cross link domains
Elastomeric domains
VARIOUS ELASTOMERIC PROTEINS (see Tatham & Shewry, 2000)
RESILIN
Very elastic protein of insect cuticle (Weis-Fogh, 1960)
Very insoluble
>33% Gly, 9-16% Pro, No Met, Cys, HydroxyPro
Resilin - putative crosslinks
(Anderson)
Presumably derived from Tyr
SILK FIBROIN
•Main protein of silk (75%); the other major protein is sericin
•Very strong fibre; resistant to tension (non-stretchy) but flexible
•Very simple aa composition: ~46% Gly, 29% Ala, 12% Ser
(c.f. sericin: 37% Ser, 17% Gly, 16% Asp)
•b-pleated sheet; close to fully extended (~6.9Å repeat distance)
•Sheets pack on top of each other; no covalent crosslinks; Hbonds, V de W's forces and hydrophobic interactions stabilise
Repeating unit in silk fibroin
Fibroin polypeptide chain: Mr ~ 370,000;
~65% 'crystalline', ~33% amorphous;
crystalline has ~50 repeats of 59 aa unit:
-Gly-Ala-Gly-Ala-Gly-Ser-Gly-Ala-Ala-Gly-[Ser-Gly-Ala-Gly-Ala-Gly]8-Tyr-
b-PLEATED SHEET
b-PLEATED SHEET
SILK FIBROIN
KERATIN REVISION
You have come across keratin in several previous lecture courses,
including Cellular Biochemistry (lectures by Wallis and Bacon) and
ETS (lectures by Woolfson) and so should already know the answers
to most of the following questions, Use them to revise and if
necessary expand the topic. I shall run through them quickly in the
lecture if time permits.
1.How many keratin genes and types are there in humans?
2.Where do keratins occur? What is their relation to the cytoskeleton.
3.What is the main secondary structure found in keratin?
4.Keratin super secondary structure comprises coiled coils. What
does this mean? What is the significance of "heptad repeats" for this?
KERATIN - REVISION (cont.)
5. How long are individual keratin molecules? How are they
incorporated as subunits into keratin superstructures? What is the
significance of "acidic" and "basic" keratins in this respect?
6. What are the main crosslinks in keratin? How can they be broken to
partially solubilise the protein? How does increased crosslinking
affect keratin's properties?
7. Keratin is the main component of hair. How are individual keratin
molecules organised in a hair fibre?
8. Changes in keratin structure underlie temporary and permanent
waving of hair. How?
9. If your hair grows at one cm per month, how many turns of alpha
helix per second does this represent?
10.Epidermolysis Bullosa Simplex is an inherited human disease.
What are its symptoms? What is its molecular basis? Is it dominant or
recessive? How frequent is it?
The a-helix
Keratin Superstructure
Wool fibre (200,000 Å)

Packed dead cells (20,000 Å)

Macrofibril (2,000 Å)

Microfibril (80 Å)

Protofilaments (20 Å)

Alpha helix (5 Å)
ORGANIZATION OF KERATIN FIBRILS