NMR studies on domain diffusion and alignment in modular GB1 repeats

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• Modular proteins are composed of distinct domains linked by flexible regions.
• Understanding domain dynamics in modular proteins is crucial for deciphering their function.
• Previous studies often assume independent domain behavior in such systems.

Purpose of the Study:

• To investigate the rotational diffusion and long-range angular ordering of individual domains in tandem repeat modular proteins.
• To determine if flexible linkers abolish distinct domain behaviors or allow for long-range influences.

Main Methods:

• Utilized a model system based on the GB1 domain to construct tandem repeat proteins.
• Employed Nuclear Magnetic Resonance (NMR) relaxation parameters and residual dipolar couplings to measure domain properties.
• Analyzed diffusion tensor anisotropy and rotational correlation times for N-terminal (NTD) and C-terminal (CTD) domains.

Main Results:

• Each domain within the tandem repeat protein displayed unique rotational diffusion and alignment properties, despite similar protein-solvent interfaces.
• The N-terminal domain (NTD) showed diffusion tensor anisotropy (D(‖)/D(⊥)) of 1.5-1.6, while the C-terminal domain (CTD) exhibited a higher value of 2.0-2.2.
• Differences in rotational correlation times and magnetic alignment (D(a) values) were observed between the NTD and CTD, even with flexible linkers of varying lengths (3-24 residues).

Conclusions:

• Distinct rotational diffusion and long-range angular ordering behaviors persist in individual domains of modular proteins, even with highly flexible linkers.
• These findings suggest that domain-specific properties and long-range influences can be maintained in modular protein systems, irrespective of linker length and without direct domain-domain interactions.
• The study highlights the complexity of protein dynamics in modular systems, challenging assumptions of complete domain independence.