Which amino acid is least likely to be found in one of the transmembrane domains of GPCR43?

• A. Valine
• B. Phenylalanine
• C. Leucine
• D. Aspartic acid

Answer: (D)

Verified step by step guidance

1. Understand the structure of transmembrane domains in GPCRs: Transmembrane domains are typically composed of hydrophobic alpha-helices that span the lipid bilayer. These regions are rich in nonpolar, hydrophobic amino acids to interact favorably with the hydrophobic environment of the membrane.
2. Analyze the properties of the given amino acids: Valine, Phenylalanine, and Leucine are all nonpolar, hydrophobic amino acids, making them suitable for incorporation into transmembrane domains. Aspartic acid, however, is polar and negatively charged, which makes it hydrophilic and less likely to be found in the hydrophobic environment of the membrane.
3. Recall the principle of hydrophobicity: Hydrophobic amino acids are favored in transmembrane regions because they minimize unfavorable interactions with the aqueous environment. Hydrophilic amino acids, like Aspartic acid, are typically found in regions exposed to water, such as extracellular or intracellular loops.
4. Consider the functional role of GPCRs: GPCRs (G-protein-coupled receptors) rely on their transmembrane domains to anchor them within the lipid bilayer and facilitate signal transduction. Hydrophobic amino acids contribute to the stability and proper folding of these domains.
5. Conclude based on the properties of Aspartic acid: Aspartic acid's hydrophilic nature makes it least likely to be found in the transmembrane domain of GPCR43, as it would disrupt the hydrophobic environment required for proper membrane integration.