Hydrophobic proteins and water: If a protein were built exclusively from nonpolar amino acids, how would it interact with water?

Introduction / Context:
Protein–water interactions drive folding and function. Nonpolar amino acids (for example, leucine, isoleucine, valine, phenylalanine) avoid contact with water, a phenomenon underlying the hydrophobic effect.

Given Data / Assumptions:

• Hypothetical protein composed exclusively of nonpolar side chains.
• Environment: aqueous solution.
• No detergents or chaperones present.

Concept / Approach:
Water forms a hydrogen-bonded network; nonpolar surfaces disrupt it without compensating interactions. To minimize this disruption, nonpolar residues cluster together, reducing exposed hydrophobic surface area. Thus, an all-nonpolar protein would be extremely insoluble and “repelled” by water, aggregating or partitioning into nonpolar phases.

Step-by-Step Solution:
Identify the side chain chemistry: nonpolar = hydrophobic.Predict solubility: poor in water, tendency to aggregate.Choose the option indicating repulsion from water.

Verification / Alternative check:
Membrane proteins bury nonpolar regions within lipid bilayers and expose polar regions to water; all-nonpolar sequences are typically membrane-embedded or insoluble aggregates.

Why Other Options Are Wrong:

• Attracted to water/buffer behavior: Requires polar/ionizable groups.
• Spontaneous lipid membrane formation: Lipids, not proteins, form bilayers.

Common Pitfalls:
Confusing hydrophobic aggregation of proteins with membrane self-assembly by amphipathic lipids.

Final Answer:
It would be repelled by water (strongly hydrophobic).