Proteins, Enzymes, and Structural Biology
Protein folding as a landscape problem
Energetics and dynamics
Protein folding is best viewed as motion on an energy landscape with multiple intermediates and competing minima. Native structure is stabilized by a collective balance of hydrophobic collapse, hydrogen bonding, electrostatics, and solvent effects.
Seminal idea
The sequence determines the fold under many conditions, but the folding pathway and cellular context strongly influence the realized ensemble.
Enzymatic catalysis
How enzymes accelerate reactions
Enzymes lower activation barriers by stabilizing transition states, orienting substrates, excluding water, and coupling conformational changes to chemistry. Catalytic efficiency can be approximated by the rate enhancement .
What is the main reason enzymes speed up reactions?
Enzymes accelerate reactions by lowering the activation barrier, not by changing the thermodynamic equilibrium.
Correct answer: They lower the activation energy
What structural problem is being actively transformed by cryo-electron microscopy?
Cryo-EM has made it possible to resolve large and flexible complexes that are difficult for crystallography.
Correct answer: High-resolution determination of macromolecular complexes
Structure determination methods
Major structural methods
X-ray crystallography
- High atomic resolution for crystals
- Requires crystallization and may miss dynamics
Cryo-EM
- Excellent for large complexes and multiple states
- Lower resolution can remain challenging for small proteins
Which technique is especially powerful for observing multiple conformational states of large macromolecular assemblies?
Cryo-EM can capture heterogeneous conformational populations in large complexes.
Correct answer: Cryo-electron microscopy
Define allostery in one sentence.
Allosteric effects arise from conformational coupling across a protein or complex.
Correct answer: Allostery is regulation at one site by a perturbation at a distant site