Structure and backbone dynamics of a microcrystalline metalloprotein by solid-state NMR

Area of Science:

• Biophysics
• Structural Biology
• Biochemistry

Background:

• Determining the structure and dynamics of large metalloproteins is challenging.
• Solid-state Nuclear Magnetic Resonance (NMR) is a powerful technique for studying biomolecules.
• Ultrafast magic angle spinning (MAS) with 1H detection enhances NMR sensitivity and spectral resolution.

Purpose of the Study:

• To develop and validate a novel solid-state NMR approach for improved structural and dynamical characterization of large metalloproteins.
• To apply this method to the enzyme Copper, Zinc Superoxide Dismutase (SOD).
• To leverage paramagnetic relaxation enhancements for precise structural constraint determination.

Main Methods:

• Utilized solid-state NMR with 1H detection under ultrafast magic angle spinning (MAS).
• Acquired extensive sets of 15N and 13C nuclear relaxation rates.
• Employed paramagnetic relaxation enhancements by comparing Cu(+) (diamagnetic) and Cu(2+) (paramagnetic) forms of SOD.
• Applied Gaussian Axial Fluctuation (GAF) analysis to relaxation rates for dynamics determination.

Main Results:

• Achieved a twofold improvement in structural precision when paramagnetic relaxation enhancements were combined with 1H-1H distance restraints.
• Determined site-specific order parameters and timescales of motion.
• Interpreted dynamics in relation to protein backbone structure and metal ion binding.

Conclusions:

• The novel solid-state NMR approach significantly enhances the structural and dynamical determination of large metalloproteins.
• Paramagnetic relaxation enhancements provide valuable structural constraints.
• GAF analysis reveals insights into protein dynamics, revealing motions on the timescale of overall molecular tumbling.