Quaternary structure refers to the structure of protein complexes containing multiple protein subunits. It is important because oligomeric proteins are involved in key biological processes like metabolism and signal transduction. Determining quaternary structure helps understand how proteins work and allows for hypotheses about controlling or modifying them. Common techniques used include X-ray crystallography, electron microscopy, and nuclear magnetic resonance spectroscopy. X-ray crystallography uses X-ray diffraction from protein crystals to determine atomic structure, while NMR spectroscopy analyzes nuclear properties to determine interatomic distances and overall structure in solution.

1. QUATERNARY STRUCTURE
DETERMINATION

2. Quaternary Structure;
 Exists in proteins consisting of ;
1) two or more
2) identical or different
3) Multiple folded polypeptide chains (subunits)
4) Held together by hydrogen bonds and van der Waals forces between nonpolar side chains
 Called oligomers (consisting of multiple protein subunits)

3. Why is quaternary Structure
important?
 Oligomeric proteins are involved in various biological processes, such as
 metabolism,
 signal transduction,
 Chromosome replication
 Conservation of valuable resources in the creation of a large protein by repeating
the synthesis of a few polypeptide chains many times rather than synthesizing one
extremely long polypeptide chain.

4. STRUCTURE DETERMINATION helps
understand;
 How a protein works
 To create hypothesis on
1. How to affect it
2. control it
3. modify it
 The study of drug design and protein design etc

5. Techniques Used
 The quaternary structure is usually determined by X-rays Crystallography
 When the Crystallographic data were difficult to obtain, Electron
Microscopy provided the information
 Nuclear Magnetic Resonance (NMR)
It is relatively simple to determine the multisubunit composition of a
quaternary protein experimentally. By disrupting the interactions that hold
multisubunits together, it is also possible to establish the molecular weight of
each by using size-exclusion chromatography. If the method is repeated
without bond disruption, the composition can be determined by using simple
mathematics.

6. X-Ray Crystallography
 Powerful technique for ;
1. Visualizing the structure of protein.
2. Identifying the atomic and molecular structure of a crystal.
 -Uses the principles of X-ray diffraction to analyze the sample, but is
done in many different directions so that the 3D structure can be built
up.
WHY x-rays?
1. Wavelengths similar to the size of atoms
2. Smaller wavelength than visible light
3. higher energy
4. penetrate matter more easily than can visible light.

9. NUCLEAR MAGNETIC RESONANCE (NMR)
 NMR involves the quantum-mechanical properties of the central
core ("nucleus") of the atom.
 This information can be used to determine the distance between
nuclei. These distances in turn can be used to determine thE overall
structure
 Only method that allows the determination of three-dimensional
structures of proteins molecules in the solution phase
 For proteins in the size range between 5 and 25 kD

10. • Protein structure determination by NMR can be performed by
automated methods.
• The CYANA software combines peak picking, assignment, and
structure calculation.
Fully automated methods can yield structures with accuracy better
than 1 Å.
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12. THANK YOU