B2.023 Mutations that Alter Proteins: A Variety of Outcomes

Question 1

what kinds of protein parameters can mutations alter?

Answer 1

folding/stability, concentration, location, post-translational modification, function

Question 2

what factors affect alteration of protein concentration?

Answer 2

gene expression and protein degradation

Question 3

what measure is affected by protein concentration?

Answer 3

vmax of catalysis or transport

Question 4

what example was discussed with reference to post translational modifications of proteins?

Answer 4

cleaving of trypsinogen by enteropeptidase in small intestine to activate it into trypsin

trypsin then catalyzes activation of other enzymes

Question 5

how do proteins bind to ligands?

Answer 5

specific amino acid interactionds, side chain or backbone

Question 6

how can mutations alter binding?

Answer 6

affinity (how tightly it binds)

specificity (which lingand is bound most tightly)

Question 7

how do we quantify binding affinities?

Answer 7

association reaction and dissociation reaction constants Ka and Kd

Question 8

why is Kd particularly useful?

Answer 8

Kd=[L] when [P] = [PL] so you can tell how much ligand needs to be present to bind 50% of the protein (units M)

Question 9

how do you plot ligand/protein binding?

Answer 9

[ligand] vs fraction bound

can be linear (hyperbolic shape) or log (sigmoidal shape)

Question 10

how can a mutation in amino acid physically decrease binding stability in vitamin D resistant rickets?

Answer 10

if a smaller amino acid is subbed, lacks stabilizing interaction

Question 11

how can a mutation in an ion channel protein affect the heart?

Answer 11

long QT syndrome can result from Na+ channels not opening/closing properly

Question 12

how does HIV resist drugs?

Answer 12

mutations in the HIV protease can inhibit the drugs ability to bind to the active site, making the drug ineffective against that from of HIV

Question 13

how do we get around drug resistance in HIV protease?

Answer 13

treat HIV with a cocktail of 8 drugs

Question 14

what is protein moonlighting?

Answer 14

proteins can have more than one function

Question 15

what are 4 complicating factors in the study of protein function?

Answer 15

1. moonlighting
2. normal polymorphisms can interact differently with the environment
3. environment includes other proteins
   - partners can have exacerbating or compensatory mutations
4. current computer algorithms predict good/bad for missense mutations, but risk could be intermediate