Question

What type of stabilizing interaction could there be between the side chains of glutamate and lysine? Please explain why as well.

-Salt bridges

-Hydrophobic interactions

-Hydrogen bonds

Answer 1

[1]. Salt bridges: are non-covalent bonds between oppositely charged residues that are close enough to each other to experience electrostatic attraction.

Salt bridges in proteins:

• In proteins, salt bridge often arises from the interaction of anionic carboxylate (RCOO⁻) of either aspartic acid or glutamic acid with the cationic ammonium (RNH₃⁺) from lysine or the guanidinium (RNHC(NH₂)₂⁺) of arginine.

Lysine-Glutamate Salt Bridge Interaction (LYS-GLU):

Only when the side chains of glutamate and Lysine are at a smaller separation, salt bridge interaction is significant

With the increase in distance, this electrostatic interaction starts to diminish quickly. [Refer coloumb’s law; where it can be clearly seen that the electrostatic force is inversely proportional to the square of distance]

[2]. Hydrogen bond: is a weak electrostatic attraction between a hydrogen (H) atom which is bonded to a more electronegative atom (N, O, F) and another adjacent atom bearing a lone pair of electrons.

Hydrogen bond in LYS-GLU:

The Hydrogen bond between Glutamate and Lysine is more stable here because of the additional salt bridge interaction present.

è Note: Salt bridge interaction is more stable than Hydrogen bond interaction

[3]. Hydrophobic interaction: Weak interactions between non-polar molecules (water hating)

Hydrophobic interactions between LYS-GLU;

If we observe the side chains of Lysine and Glutamic acid, both of them are hydrophilic in nature (polar, water loving). Though both of them possess –CH2-CH2- group in their side chain, their contribution is insignificant in comparison to the hydrophilic part interaction.

Conclusion: There exists salt bridge and Hydrogen bond interaction and No hydrophobic interaction between LYS and GLU