Consider a protein in which a negatively charged glutamic acid side chain (pKa=4.2)(pKa=4.2) makes a salt bridge (ion-ion interaction) with a positively charged histidine side chain (pKa=6.5)(pKa=6.5). Do only part B. Part ADo you predict that this salt bridge will become stronger, become weaker, or be unaffected as pH increases from pH = 6.9 to pH = 7.9?The salt bridge will become stronger.The salt bridge will become weaker.The salt bridge will be unaffected.SubmitPrevious AnswersCorrectAt pH = 6.9 the glutamic acid (Glu) side chain will carry a charge of ~ -1 (at 3 pH units above the pKa for Glu, the side chain will be almost fully ionized); whereas thehistidine (His) side chain will carry a charge of < +0.5 (at pH = pKa the charge on His would be +0.5; since pH = 6.9 is above its pKa, it will carry less (+) charge as itbecomes more deprotonated). As the pH increase to 7.9, the charge on Glu will remain ~ -1 and the charge on His will decrease; thus, this salt bridge is predicted tobecome weaker as pH is raised from 6.9 to 7.9.Part BJustify your answer with calculations of partial charges on these amino acid side chains at pH = 6.9. (Hint: Consider lessons from Coulomb's law, and the Henderson-Hasselbalchequation.)Express your answers using two significant figures separated by a comma.VE ΑΣΦ0.0022,2.5?

The Henderson-Hasselbalch equation relates the pH of a solution to the pKa of a weak acid and its…

Consider a protein in which a negatively charged glutamic acid side chain (pKa=4.2)(pKa=4.2) makes a salt bridge (ion-ion interaction) with a positively charged histidine side chain (pKa=6.5)(pKa=6.5).

Consider a protein in which a negatively charged glutamic acid side chain (pKa=4.2)(pKa=4.2) makes a salt bridge (ion-ion interaction) with a positively charged histidine side chain (pKa=6.5)(pKa=6.5).

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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A cytosolic protein has an important alpha amino group. The pKa of this group is approximately 8 when exposed to water outside of a protein. 1. What would happen to the pKa if this group was instead buried in the hydrophobic interior of the protein? Explain. 2. Let’s say in the hydrophobic interior of the protein, the group forms an ionic bond with a carboxylate group of the side chain of a charged Asparagine residue. How would the pKa of this alpha amino group compare with the pKa of the alpha amino group in the hydrophobic interior of the protein without a nearby Asparagine residue to form this ionic bond? Explain.
Theoretical and experimental data show that in many cases the ionic and hydrogen-bonding interactions to ΔH for protein folding are close to zero. Provide an explanation for this result.
Consider the phenolic hydroxyl group of a particular Tyr residue in a protein. Suppose the hydroxyl group in the unfolded protein in aqueous solution, where the group is exposed to H2O, has a pKa of 10.0. If that group is found in a hydrophobic environment in the interior of the protein when the protein is folded into its native tertiary structure, would you expect the pKa of the phenolic hydroxyl to be higher or lower in the folded protein interior than in H2O? Explain your reasoning.
Consider protein folding that results when the following components interact: Where the solution is at a pH of 7, green (thick-dotted line) represents aspartic acid (R group contains a carboxylic acid with pKa = 4), orange (thick-solid line) represents lysine (R group contains an amine with pKa = 10), and blue (thin-solid line) represents hydrophilic groups. Rank the three complexes in order from lowest to highest dissociation constants Kd (low Kd values correspond to good binding constants and low energy, while high Kd values correspond to low binding constants and high energy) as determined by intermolecular charge-charge interactions. For those complexes with charge-charge interactions being equal, look at the possibility for the formation of hydrogen bonds via carboxylic acid dimers (only possible when the carboxylic acid is protonated) which are low energy structures.
Consider the following peptide to answer the questions below: A M A K K E S H I F T A I D E What is the total charge of this peptide at pH = 5? What is the N terminal amino acid (full name)? C terminal amino acid? How many fragments would result if this peptide underwent proteolytic cleavage with V-8 protease and what are these fragments (list them)? Would this peptide be a candidate to form an alpha helix? Why or why not
What would you predict about the ratio of hydrophilic to hydro- phobic amino acid residues in a series of monomeric globular proteins that range in size from a molecular weight of 10,000 g/mole to a molecular weight of 100,000 g/mole? Note that the volume of a sphere is 4/3nr³, while the sur- face area of the outside of a sphere is 4nr². How would your prediction change if the monomeric proteins were fibrous instead of globular?
Suppose you have a solution of a protein, which contains a specific Tyr residue that has an actual (measured) pKa of 8.8. The protein binds a ligand by several noncovalent interactions, one of which is a hydrogen bond in which the Tyr phenolic hydroxyl group must serve as a hydrogen bond donor. Calculate the percentage of the protein molecules in which that tyrosyl residue's phenolic hydroxyl group could serve as a hydrogen bond donor at pH 8.5
Based on the pK, table for amino acids (Table 1.1), draw the structures with net charge, and the equilibria representing the complete deprotonation of aspartate. Table 1.1 Name pK pk2 pKR Glycine Alanine 2.4 9.8 2.3 9.7 Valine 2.3 2.4 9.6 Leucine 9.6 Isoleucine 2.4 9.7 Methionine 2.3 9.2 Phenylalanine Proline Serine 1.8 9.1 2.0 10.6 2.1 9.2 Threonine 2.6 10.4 Cysteine Asparagine Glutamine 1.8 10.8 8.3 2.0 8.8 2.2 9.1 Tyrosine Tryptophan Aspartate Glutamate 2.2 9.1 10.9 2.4 9.4 2.0 2.2 10.0 3.9 9.7 4.3 Histidine 1.8 9.2 6.0 10.8 Lysine Arginine 2.2 9.2 1.8 9.0 12.5
A protein hypothetically consists of two polypeptide chains with the given sequences in the picture. Based on the said sequences, a. Do you think it is possible that interchain disulfide bonds is present in the protein? Explain. b. Do you think it is possible that intrachain disulfide bonds is present in the protein? Explain.
The major difference between a protein molecule in its native state and in its denatured state lies in the number of conformations avail- able. To a first approximation, the native, folded state can be thought to have one conformation. The unfolded state can be estimated to have three possible orientations about each bond between residues. (a) For a protein of 100 residues, estimate the entropy change per mole upon denaturation. (b) What must be the enthalpy change accompanying denaturation to allow the protein to be half-denatured at 50 °C? (c) Will the fraction denatured increase or decrease with increasing temperature?
1. Consider the following α helix from myoglobin at pH 7. Gln-Gly-Ala-Met-Asn-Lys-Ala-Leu-Glu-His-Phe-Arg-Lys-Asp-Ile-Ala-Ala-Lys-Tyr(a) Label amino acids in the polypeptide above as follows: p for polar and uncharged, np for non polar, – for negatively charged, and + for positively charged.(b) How many complete turns are there in this helix?(b) Which side chains are likely to be on the side of the helix that faces the aqueous solvent? Why?(c) Which side chains are likely to face the interior of the protein? Why?
Histidine is an amino acid containing an ionizable group in its side chain. This ionizable group has a pka of 6.0, meaning that His is in its deprotonated form at physiological pH (7.0-7.4). However, His is included in the positively charged amino acid category. Calculate the ratio of deprotonated/protonated His at pH 7.0, and use your answer to justify why this amino acid is included in the positively charged amino acid category. Show all work for full credit.