2 - Protein structure Flashcards
Give the six hierarchical layers of hair
- Packed dead cells
- Cells packed with macrofibrils
- Microfibrils made with microfibrils that are cemented together by S-rich protein matrix
- Microfibrils composed of 4 protofibrils
- Each protofibrils is composed of a linear series of head-to-tail aligned keratin ‘coiled coils’
- Each coiled coil is a heterodimer of Type I and II alpha-keratin
What determines the degree of curliness in hair?
The amount of S cross bridges between microfibrils
Describe a coiled-coil
A helix with slightly tighter repeat per turn than alpha helices.
3.5 residues per turn vs. 3.6
Helix is inherently coiled
Why is a coiled coil considered a heptad repeat?
Because there are 3.5 residues per turn. Therefore 7 until you’re back at your starting position.
What function does the coiled nature of a coiled coil give?
It allows ridges of one helix to insert into grooves of the other
Fibrinogen is a 3-4 strand ____ structure. It is cleaved to form fibrin, which has striations __ the length of fibrin.
Fibrinogen is a 3-4 strand coiled-coil structure. It is cleaved to form fibrin, which has striations 1/2 the length of fibrin.
Give the structure of collagen.
- Triple helix: three helical polypeptides wound around each other
- Gly-X-Y repeat (each chain)
- Gly is needed to allow triple helix packing
- X: 30% proline
- Y: 33% 4(R)-hydroxyproline (Hyp)
What is the most important qualities of collagen?
- Tensile strength for tissue and organs
At what parts of collagen’s sequence does it show the most heterogeneity (variability)?
The X and Y parts (not the Gly parts)
There are extremes in conformation for imino rich vs . amino rich regions
What is the equivalent for elastin in insects?
Resilin (for motility)
Give the basic structure of human tropoelastin
Alternating hydrophobic and cross linking domains
How does resilin store energy when it is bent by muscle in insects?
Energy input converts disordered elastic domains to beta-turns, allowing energy storage.
True or false. Spider silks are stronger and tougher than any synthetic material?
True
What gives the different spider silks their differing properties?
Highly variable primary structure
What did Raman spectroscopy reveal about spider silks?
Their secondary structures
Eg. alpha and beta sheet content differs
One gland produces heterogeneous and disordered silk
What are the two predominant theories in silk building?
- Micelle theory (physical shear is exerted on micelles, inducing beta sheet formation)
- Liquid crustal theory (Producing a liquid crystalline form and squeezing it into oriented beta sheets.
In spider silk, strength comes from ____ domains. Elasticity from ____ regions.
Strength: beta-sheet domains
Elasticity: disordered regions
Alpha helices may make it more ‘tough’
Outline the differences in glycine/proline content for fibrinigous and elastic protein domains.
Fibrinigous domains: Low gly, low pro
Elastic: High gly, moderate pro
What are motifs?
In a chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a supersecondary structure, which also appears in a variety of other molecules. Motifs do not allow us to predict the biological functions: they are found in proteins and enzymes with dissimilar functions.
They lack a (full) hydrophobic core. Domains are the simplest self contained units. Domains (folds) are made up of motifs
True or false? Nature is conserved when it comes to folding proteins?
True. There are about 1200 known folds, but half of the known structures fall into only 20 fold groups!
Fibrous proteins are to ___ structure as globular proteins are to ___ structure
Fibrous proteins are to ‘secondary’ structure as globular proteins are to ‘tertiary’ structure
What is the hallmark of elastin assembly?
Coacervation mechanism
This where colloidal elastin droplets are electrostatically attracted to form branched fibrillar structures.
Fibrillin and fibulin can associate with coalesced species to aid in structure and rigidity.
What is a major function of resilin in flying insects?
It is stretched by muscle, converting energy for spring like release that saves more than 10% of energy per stroke
Give the basic conformation of each exon of resilin
Exon I: disordered when relaxed
Exon II: Chitin binding domain, alpha helical
Exon III: Disordered when relaxed
