Dynamics in the Intact fd Bacteriophage Revealed by Pseudo 3D REDOR-Based Magic Angle Spinning NMR

Area of Science:

• Biophysics
• Structural Biology
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• Understanding the relationship between structure, motion, and function in biological systems is crucial.
• Nuclear Magnetic Resonance (NMR) is a powerful technique for probing atomic-scale dynamics.

Purpose of the Study:

• To develop and validate an automated NMR protocol for measuring effective ¹³C-¹⁵N dipolar coupling constants.
• To quantify the order parameters and dynamics of C-N bonds in fd-Y21M filamentous bacteriophage coat proteins.

Main Methods:

• Utilized magic-angle spinning NMR with a novel combination of three pseudo three-dimensional experiments.
• Integrated a rotational echo double resonance (REDOR) dephasing block with three complementary ¹³C-¹³C mixing schemes (dipolar-assisted rotational resonance, through-bond transfer-based double quantum/single quantum correlation, and radio frequency driven recoupling).

Main Results:

• Accurately measured effective ¹³C-¹⁵N dipolar coupling constants for multiple spin pairs simultaneously.
• Quantified order parameters for numerous C-N bonds in the coat protein of intact fd-Y21M filamentous bacteriophage.
• Revealed submillisecond time-scale dynamics, including uniform small-amplitude motion (∼30°) in the helical region and high flexibility in the N-terminus.

Conclusions:

• The helical coat protein region exhibits constrained motion, while the N-terminus is highly flexible.
• Reduced mobility of C-terminal lysine sidechains suggests interaction with single-stranded DNA.