Helical Packing in Membrane Proteins

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Why are proline kinks important in membrane proteins?

To prevent the formation of binding sites
To facilitate the packing of helices in a parallel orientation
To allow side chains to be placed more freely (correct)
To increase the rigidity of transmembrane helices

What is the purpose of partially unwound helices in transmembrane proteins?

To allow side chains to be positioned more freely (correct)
To restrict the movement of side chains
To prevent interactions with other membrane proteins
To increase the stability of the helices

Why do helices prefer to pack at an angle to one another?

To increase the rigidity of the helices
To restrict the exposure of backbone residues
To facilitate parallel packing which is energetically favorable
Because they can only interact well for a limited number of turns (correct)

What happens when helices are packed in a parallel orientation?

They cannot pack well due to diagonal orientation of side chain ridges (D) Signup and view all the answers

How can 2 short helices mimic one long helix in multi-spanning TM proteins?

By turning back after partially crossing the bilayer (A) Signup and view all the answers

What is the consequence of helices diverging too far to interact well?

It results in poor interaction between neighboring helices (A) Signup and view all the answers

Which of the following statements about helix packing is true?

All of the above statements about helix packing are true. (D) Signup and view all the answers

What is the significance of the GXXXG motif in alpha helices?

The GXXXG motif brings two glycine residues to the same face of the helix, creating a groove for another helix to approach closely. (C) Signup and view all the answers

Which of the following statements about monotopic membrane proteins is correct?

Monotopic membrane proteins have small hydrophobic domains that interact with only one leaflet of the membrane bilayer. (D) Signup and view all the answers

What is the significance of conserved glycine residues in transmembrane helix-helix interactions?

Conserved glycine residues provide flexibility and allow closer helix-helix interactions. (D) Signup and view all the answers

Which of the following statements about pi (π) helices is correct?

Pi helices involve hydrogen bonding between the C=O of residue i and the NH of residue i+5. (A) Signup and view all the answers

What is the primary reason why proline residues are not commonly found in the interior of protein secondary structures?

Proline's amide nitrogen lacks a hydrogen atom, preventing it from participating in hydrogen bonding. (B) Signup and view all the answers

What effect does the presence of a proline residue have on the structure of an α-helix?

It introduces a kink or distortion in the helix due to the inability of proline to participate in hydrogen bonding. (A) Signup and view all the answers

Which of the following statements about the peptide bond configuration is correct?

The cis configuration of the peptide bond is often found in β-turns, while the trans configuration is more common in α-helices and β-sheets. (C) Signup and view all the answers

Which of the following statements about helix packing in proteins is correct?

Helix packing is primarily driven by hydrophobic interactions between the side chains of non-polar residues. (C) Signup and view all the answers

Which of the following statements about partially unwound helices is correct?

Partially unwound helices are characterized by a change in the hydrogen bonding pattern, leading to a local disruption in the helical structure. (B) Signup and view all the answers