Ch. 4.3 - 4.4: Structure

homooligomer

a protein made of multiple identical subunits

heterooligomer

a protein made of multiple different subunits

3 most common oligmeric structures

dimers; then monomers; then tetramers

are homo- or hetero- oligomers more common?

homo

types of symmetry in quat structure

cyclic; dihedral; tetrahedral; octahedral; isocahedral

quat structure cause

mainly hydrophobic effect

how common are multiprotein complexes?

~80% of proteins

molecular machine

elaborate enzymatically active complex of numerous proteins; made to produce mechanical movement in response to specific stimuli

molecular machine examples

ATP synthase; flagellar motors

molecular breathing

conformational flexibility; ability to shift in response to ligand bonding; enables diffusion of small molecules

intrinsically disordered protein

lack defined sec or tert structure; often signalling & regulation proteins; develop structure upon binding. many capable of binding multiple ligands

residues in intrinsically disordered proteins

high in polar 7 ionized residues; low in bulky hydrophobic residues

why are proteins susceptible to denaturing?

mainly stabilized by weak nonbinding forces

4 conditions that can cause denaturation

heat; pH; detergents; chaotropic agents

mercapthoethanol role in denaturation

reduces disulfide bonds, cleaving them

how long do proteins take to fold?

less than a few seconds; as little as microseconds

why do proteins fold quickly?

they fold via directed pathways; earlier steps stabilize & constrain later steps

stages in protein folding

sec structure starts; hydrophobic collapse creates molten globule; tert structure forms as H2O is excluded from hydrophobic core

molecular chaperone

a protein that binds to non-folded proteins, preventing improper association of exposed hydrophobic regions. keep folding proteins from getting trapped in false minima

classes of molecular chaperone

hsp70 family in prokaryotes; trigger factor in prokaryote ribosomes; molecular chaperones in both; hsp90 family in eukaryotes

5 diseases caused by misfolding

alzheimers; parkinsons; huntingtons; fibrinogen amyloidosis; lysozyme amyloidosis