Tertiary Structure Determination: Circular Dichroism vs. Other Methods

Proteins with α-helices and β-strands rely on specific techniques for tertiary structure analysis. The correct method among the options is nuclear magnetic resonance spectroscopy.

Correct Answer

(C) nuclear magnetic resonance spectroscopy​

Nuclear magnetic resonance (NMR) spectroscopy provides atomic-level details of a protein’s three-dimensional fold by analyzing nuclear spin interactions in a high-field magnet, resolving distances and angles in tertiary structures with α-helices and β-strands. This technique excels for proteins up to 50-100 kDa in solution, offering precise mapping of helix-strand packing without crystallization.​

Option Analysis

Circular dichroism (CD) spectroscopy primarily assesses secondary structure content, such as α-helix (negative band at 222 nm) and β-strand (positive at 195 nm) proportions, through differential light absorption by chiral environments. It classifies overall folds but lacks atomic resolution for detailed tertiary interactions like side-chain packing.​

Mass spectrometry determines molecular weight, post-translational modifications, and sometimes topology via footprinting or hydrogen-deuterium exchange, but it does not directly yield 3D coordinates of tertiary structure.​

UV spectroscopy at 280 nm measures aromatic residue absorbance for concentration or folding states, providing no specific tertiary or secondary structural insights.​

Key Techniques Comparison