Protein Imaging

Question 1

What are the determinants of resonance line positions?

Answer 1

local electronegativity
type of groups
torsion angles.

Question 2

What shifts are produced by; 
aromatic side chains, 
H bond formation, 
alpha helices, 
beta sheets?

Answer 2

• In plane = low / above = high
• low
• low
• high

Question 3

What can shifts tell us about folds?

Answer 3

Hydrophobic cores contain close packing of hydrophobic AAs.
Aromatic AAs are often conserved in fold families.
Methyl groups in these will be high field shifted in folded state but on unfolding the signature resonances will be gone.

Question 4

Why are we not able to measure large structures with NMR?

Answer 4

Increased Mr –> lower S/N, increased overlap of peaks - large number of peaks in limited spectral area.

Question 5

What is the S2 value?

Answer 5

Indicator of local mobility

0 = fully mobile 
1 = fully rigid.

Question 6

What are the main issues arising from crystallisation?

Answer 6

• highly purified protein
• highly concentrated protein
• slowly reach eqm (avoid precipitation)
• trial & error to identify optimal conditions.