Protein structure is measured using different techniques depending on the size of the protein and the desired level of detail.
Methods for Determining Protein Structure
Here are the primary methods used:
X-Ray Crystallography
This method is used for determining the three-dimensional structure of a protein at atomic resolution. It involves these steps:
- Crystallization: Large proteins need to be crystallized, a process where the protein molecules are arranged in a highly ordered, repeating pattern.
- X-Ray Diffraction: The crystallized protein is then exposed to X-rays. The way the X-rays scatter, or diffract, as they pass through the crystal provides data on the arrangement of atoms within the protein.
- Structure Determination: By analyzing the diffraction pattern, scientists can reconstruct a three-dimensional model of the protein's structure.
Key Point: According to the provided reference, "to determine the three-dimensional structure of a protein at atomic resolution, large proteins have to be crystallized and studied by x-ray diffraction".
Nuclear Magnetic Resonance (NMR) Analysis
This technique is ideal for determining the structure of small proteins in solution.
- Nuclear Properties: NMR uses the magnetic properties of certain atomic nuclei to get information about the protein.
- Solution State: Unlike X-ray crystallography, which requires a protein crystal, NMR allows for the analysis of proteins in their natural solution state.
- Structure Determination: By analyzing how nuclei respond to magnetic fields, scientists can determine the distances between atoms and thus construct a three-dimensional structure of the protein.
Key Point: The reference states that "the structure of small proteins in solution can be determined by nuclear magnetic resonance analysis."
Comparison Table
| Feature | X-Ray Crystallography | Nuclear Magnetic Resonance (NMR) |
|---|---|---|
| Protein Size | Large Proteins | Small Proteins |
| Sample State | Crystalline | Solution |
| Resolution | Atomic Resolution | Atomic Resolution |
| Method | X-ray diffraction | Magnetic fields and nuclei properties |
Summary
In essence, the method used to measure protein structure largely depends on whether the protein is large or small and the state of the protein being studied (crystalline or in solution).
