L3-4: Proteins in Health & Disease Flashcards
What does protein structure determine?
Interactions with other proteins, biomols and small molecules ie function
How were the first protein structures determined?
X-ray crystallography
What protein structure does myoglobin and haemoglobin have?
Myoglobin- tertiary
Haemoglobin- tertiary and quaternary
What does tertiary structure determine?
The overall 3D shape
What chunks do proteins fold in?
Domains
What is structural homology?
When related amino acid sequences give proteins very similar structures
Which programs can ‘guess’ structures of unknown proteins?
ML and LLM
What is quaternary structure?
Binding with other protein chains (homo/haem interactions) and binding to small molecules/metals/cofactors
What cofactor are myoglobin and haemoglobin associated with?
Haem
How are myoglobin and haemoglobin coordinated?
-Porphyrin ring with iron
-Globin protein coordinates iron axially
-‘free’ coordination space binds gases
What is the difference between myoglobin and haemoglobin?
Myoglobin- monomer
Haemoglobin- tetramer (2 alpha and 2 beta)
When does haemoglobin bind to oxygen in lungs and then release oxygen in muscles?
High pO2 in lungs
Low pO2 in tissues
What saturation curves do myoglobin and haemoglobin have?
Myoglobin = hill curve
Haemoglobin = sigmoid cure
When does myoglobin deliver oxygen?
Acts as a monomer to deliver in low oxygen saturation
How does oxygen bind to Haemoglobin?
subunits act cooperatively, affinity changes dependent on how much oxygen bound
What is allostery?
When binding at one site affects binding at another site
What factors can oxygen affinity in haemoglobin depend on?
-chloride ions
-Bis-phosphoglycerate
-Protonation state of haem
-CO2 binding
What is the cause of sickle cell?
It is autosomal recessive so it is inherited genetically
How is the sickle cell shape obtained?
Mutation in HbB gene (E6V), which causes loss of charge meaning haemoglobin polymerises at low pO2
How is CF caused?
Mutation in CFTR gene (Cystic Fibrosis Transmembrane conductance Regulator)
How does the mutation impact people with CF?
It impacts ATP-gated anion channel that regulates Cl- in epithelial tissues so the absence of affects the balance of ions in epithelial mucosa which can cause production of thick mucus in lungs
What is phenylketonuria?
The loss or poor function of phenylalanine hydroxylase enzyme
What happens when someone has phenylketonuria?
Excess phenylalanine isnt metabolised to tyrosine so there is competition for transporters meaning it outweighs levels of other amino acids which leads to deficiencies
How is phenylketonuria managed?
No treatment but is controlled by diet
What type of disease is type 1 diabetes?
Autoimmune disease
How is diabetes caused?
It is caused by the destruction of pancreatic beta cells which stops the production of insulin
What are the main side effects of diabetes?
Hypoglycemia
Sweats that can lead to seizures
Long term damage to blood vessels
What is insulin produced as?
110 AA preproinsulin in beta cells in pancreas
What is insulin stored as in the pancreas?
Zinc-coordinated hexamers in crystals
What does insulin do?
It binds to receptors which signals cells to produce and activate glucose transporters in fat and muscle cells, it also synthesises glycogen in the liver
How was insulin first produced to treat diabetes?
Using recombination therapies using E.coli
How can bleeding be stopped when a blood vessel is injured?
Clotting
How does a clot form?
Platelets aggregate to stop bleeding
What are the 2 different pathways of clotting cascades and what are the characteristics associated with them?
Intrinsic pathway: exposed endothelial collagen
Extrinsic pathway: tissue factor release
Which factors are proteases in blood clotting?
II, VII, IX, X, XI, XII
What is Haemophilia A caused by?
An inherited deficiency of factor VIII
What is haemophilia B caused by?
Deficiency of factor IX
What is haemophilia C caused by?
Low levels of factor XI
How is haemophilia inherited?
It is X-linked so most affected people are XY
What are the symptoms of haemophilia?
Internal/external bleeding
Joint bleeding (causing permanent damage)
What is the treatment of haemophilia?
Clotting factors from blood serum are used and they are produced in chinese hamster ovary cells
What types of proteins are non-globular? give examples
Fibrous and filamentous proteins like cytoskeleton proteins
Structural proteins like keratin, silk and collagen
What are features of globular proteins that assemble into fibrous quaternary aggrangements?
Strong
Dynamic
Can interact with other proteins and DNA
What are characteristics of the cytoskeleton?
-Present in all cells
-links memb to nucleus in euks
-provides mechanical stability
-template for cell wall construction
-Dynamic network
What are the key classes of the cytoskeleton?
Microfilaments (actin)
Intermediate filaments (vimentin and keratin)
Microtubules (tubulin)
What are microfilaments primarily made up of?
Actin
What is the function of actin in microfilaments?
Actin binds and hydrolyses ATP
(ATP-actin high affinity for other actin
ADP-actin low affinity)
What ends is actin added to form microfilaments?
+ive end
What are examples of function behaviour being key to function in microfilaments?
Profilin/gelsolin sequester free actin
Myosin motors bind to actin and move
Actin branching proteins allowing filaments to join
Capping proteins to stabilise ends
How are intermediate filaments formed?
Coil-coiled proteins that may have globular ends at termini
Where do intermediate filaments exist?
Mostly cytoplasm but some nuclear and extracellular
What are the functions of intermediate filaments?
Cell adhesion
Cellular organisation
Muscle fibres
What are the 6 types of intermediate filaments?
I&II- keratins
III-vimentin and desmin
IV- alpha-internexin and synemin
V- lamins
VI- nestin and filensin
Where is alpha-keratin found?
Hair, nails, claws, feathers and skin
What is the structure of keratin?
Coiled coil stabilised by hydrophobic interactions, disulphides and dimers that multimerise into tetramers
What is the structure of vimentin?
Coiled coil, dimerises then forms anti-parallel tetramer, 8 form unit length filament forming fibrous filaments
What is the key element of neurofilaments?
alpha-internexin/nestin
What are the functions of lamins?
-Provides structure regulation of nucleus
-interacts with nuclear membrane
-sensitive to stretch
What are microtubules made of?
Alpha and beta tubulin
Where does elongation occur in microtubules?
At both ends (more rapid at +ive end)
How are protofilaments formed?
By end-to-end tubulin polymerisation
How are helical filaments formed in microtubules?
From 13 protofilaments
Where are microtubules found?
Key component of cytoskeleton and organised and nucleated at micro-tubule organising centres (MTOC)
What is a key place microtubules are found?
Centrosome
What molecular motors are associated with microtubules?
Trafficking of vesicles in the cell
Endo/exocytosis
Dynein/Kinesin
What are the proteins in myofibrils?
Actin, Myosin, Troponin, Tropomyosin, Titin
What is the biggest protein?
Titin
What are cilia made up of?
Complex microtubules
What is the role of cilia?
Motility - epithelial cells that move mucus, there are sensory cilia in hair cells
What are flagella? (How do they work in eukaryotes and prokaryotes?)
In eukaryotes they are similar to cilia and have a role in motility
In bacteria/archaea they are protein based helical filaments with motors connecting to cell membrane
What are the properties of filamentous viruses?
They have globular capsid proteins that form helical filaments and they protect the genetic material in the helix structure
What protein filaments can be found on surface of bacteria and archea?
Pilli and Fimbriae
What is a pilus?
Conjugative appendage, transfers ssDNA into host cell (mechanism of ab resistance)
What are fimbriae?
Surface attachments through adhesion on domains ends, role in biofilm formation
What are curli fibres?
Amyloid fibres produced by enterobacteria, role in biofilm formation
What structure does collagen have?
Triple helix:
2 identical a1 chains
3rd a2 with different seq
Rich in glycine, proline and hydroxyproline
Cross-linked:
Through condensation
What is silk and what can it be produced by?
Fibrous protein:
Silkworm, Hymenopetra, spiders and lacewings
What is silkworm silk made up of?
Fibroin:
Heavy & light variants
GSGAGA repeats (AAs)
Beta sheets
Disulphide links
Glycoprotein component
Sericin:
Serine rich
Beta sheet rich
H bonds to fibroin
What are the different types of spider silk?
Ampullate, Flagelliform, Tubuliform, Aciniform and aggregate
What are the mechanical properties of spider silk?
Strength as highly ductile and tensile strength
Dense
What is the structure of spider silk?
Spidroin:
repetitive glycine and alanine rich
beta strands regions interspersed with disordered regions
What are intrinsically disordered proteins?
Proteins that dont have regular tertiary structures (still stable and active)
What diseases can be caused by protein misfolding?
Alzheimers, Parkinsons, ALS, CJD and type II diabetes
What proteins are more susceptible to misfolding/aggregation?
Alpha-synuclein
Beta-amyloid
Prion
What structure do amyloids have?
A distinct cross-beta-sheet arrangement
How is BSE disease contracted?
Misfolding of the prion protein which has a role in memory
