proteins 2 Flashcards
cellular proteins
more than 1 polypeptide subunits
complex > 100 dK
oligomer
multi-subunit complex
oligomerisation states
homo-oligimer
Oligomer contains identical polypeptides
hetero-oligimer
contains non-identical polypeptides
protomers
and dimers
identical subunits of a complex
symmetrical unit
two monomers joined
obligate
permanent interaction
can’t see them happening any other way
light and heavy chains
of antibodies
non-obligate
transient
shorter interactions
RNA polymerase translating DNA temporary protein interaction
transient and permanent interfaces
transient; energetically unfavourable to have hydrophobicity
permanent: hydrophobic elements unlikely that interface will be exposed to exterior
interface
surfaces of the polypeptide chains
characteristics:
closely packed non-polar side chains: not exposed and allows hydrophobic interaction
hydrogen bonds: acceptors and donors : slight defamation in electron cloud could permit this
electrostatic : salt bridges ( hydrogen bounding + ion bounding)
protein-protein interaction
pattern recognition process: looking for the necessary element for different bonds
complex to form orientation of all different components of the different interactions
obligate interactions
hydrophobic residues present in the interface: interface will not be exposed
non polar side chain
transient oligomers
fewer non polar side chains: exposed to aqueous environments
hydrophobicity at interface
quaternary structure
Polypeptide subunits specific geometry in many oligomers= cyclic promoters symmetrically arranged
very complex structure = very complex function
sub-units are potential for:
1) expansion,
2) easier repair (if one is damaged you can swap it out)
3) alternate site of assembly vis-à-vis production
4) reduced genetic coding (vis-à-vis 1 polypeptide)
oligomer
better enzymes
protein function -
increase catalytic rate add a sub-unit
but extra complexity
protein types
Fibrous Proteins secondary structure:α-helical coiled coil
globular proteins variety of secondary linked by loops
hydrophobic protein
globular protein
haemoglobin:
4 subunits
adult: 2 alpha and 2 beta
foetal:2 alpha 2 gamma ( needs a greater affinity to oxygen then mother)
Iron 2+ binds oxygen Heam groups maintains Fe2+ in corrects state not Fe 3+
co-operativity
4 sub units held together by electrostatic bonds enable this molecule to do this
T=taut = deoxyhemoglobin
R= relaxed= oxyhemoglobin
oxygen binds with one- change in conformation-leads others to greater affinity with oxygen
haemoglobin needs to be able to bind and release oxygen
= when one changes it’s structure influences others
protein modification
particularly common post-transitional
introduced by enzymes or pathways
modifications of proteins regulators:
modifications of proteins regulators
usually reversible
phosphorylation, methylation & acetylation
regulation of destination
lipidation and glycolasition
glycosylation
the attachment of carbohydrates common PTM’s
stabilise protein when it’s extracellular: also aids in folding and role in cell to cell recognition
50% of proteins will be glycosylysed
carbohydrates are a min component whereas in proteoglycans major component
2 types of glycosylatio
N-linked NX/ST
O-linked attachment directly through S to T
2 types of glycosylation
N-linked NX/ST
O-linked attachment directly through S to T
hydroxylation
of proline and lysine essential to collagen vitamin C ( humans have lost the last enzyme with ascorbic pathways so wee can't produce are vitamin C ) required for hydroxylation defiance can lead to scurvy diet
folding and disease
structure defines function so function depends on structure
cells have developed extensive mechanism to prevent or remove misfloded proteins
folding quuality
exposure of hydrophobic residues to the environment
folding quality
exposure of hydrophobic residues to the environment
PMD’s characteristics
result from misfolding
and aggregation of cellular prion protein
can be genetic or acquired
activation of an immune response causing inflammation as an early sign of disease
best characterised PMD: the prion
result from misfolding
and aggregation of cellular prion protein
can be genetic or acquired
activation of an immune response causing inflammation as an early sign of disease
prion
adopt a number of forms:
large, insoluble fibrillary aggregates (PrPSc) - Small, soluble, protease sensitive oligomers
- Higher activity relative to weight
iatrogenic transmission
A current issue involves the spread of prions during medical intervention
Conventional methods of sterilisation of medical equipment are insensitive….
- contamination at the top involved sterilisation of electrode involving benzene, 70 % ethanol and formaldehyde vapour…
