Structural basis for the shielding function of the dynamic trypanosome variant surface glycoprotein coat

Area of Science:

• Parasitology
• Structural Biology
• Immunology

Background:

• The unicellular parasite Trypanosoma brucei evades host immunity using a dense coat of variant surface glycoprotein (VSG).
• Complete structural data for VSG has been lacking, hindering a full understanding of its protective function.

Purpose of the Study:

• To determine the complete three-dimensional structure of VSG molecules.
• To investigate the structural flexibility and dynamic behavior of the VSG coat.

Main Methods:

• Utilized high-resolution structures of individual VSG domains.
• Employed small-angle X-ray scattering (SAXS) to model complete VSG structures.
• Conducted single-molecule diffusion measurements in supported lipid bilayers.

Main Results:

• Elucidated the first two complete VSG structures, revealing domain flexibility via linker regions.
• VSG structures can adopt at least two conformations, enabling adaptation to environmental changes.
• Diffusion measurements confirmed two distinct VSG populations, indicating dynamic movement within the coat.

Conclusions:

• The VSG coat exhibits significant flexibility, allowing lateral movement and thickness variation.
• This adaptability is crucial for Trypanosoma brucei's continuous immune evasion.
• Understanding VSG structure and dynamics offers insights into parasite survival mechanisms.