Three-dimensional image reconstruction of helical aggregates of trypsin modified elongation factor EF-Tu from Escherichia coli: comparison with the reconstructed image of intact EF-Tu

Area of Science:

• Structural biology
• Biochemistry
• Molecular biology

Background:

• Elongation factor Tu (EF-Tu) is crucial for protein synthesis.
• Understanding EF-Tu's structural dynamics in polymers is key to its function.

Purpose of the Study:

• To determine the three-dimensional structure of trypsin-modified EF-Tu polymers.
• To elucidate the arrangement of EF-Tu subunits within these aggregates.

Main Methods:

• Electron image reconstruction techniques with negative staining.
• Fourier analysis and three-dimensional density synthesis.
• Analysis of cylindrical aggregates formed in ammonium sulfate solution.

Main Results:

• Cylindrical aggregates of trypsin-modified EF-Tu.GDP were observed with a diameter of ~340 Å and a repeat distance of 448 Å.
• Reconstructions revealed twofold axes perpendicular to the cylinder axis.
• A helical arrangement of EF-Tu.GDP dimers was proposed, with 15.4 subunits per turn and a pitch of 64 Å.

Conclusions:

• The study suggests a specific helical arrangement for trypsin-modified EF-Tu.GDP dimers in polymers.
• The shape of proteolyzed EF-Tu.GDP in these assemblies resembles intact EF-Tu.