The surface of the African trypanosomes

Area of Science:

• Parasitology
• Immunology
• Structural Biology

Background:

• African trypanosomes are extracellular protozoan parasites responsible for sleeping sickness.
• These parasites evade the host immune system through antigenic variation, primarily mediated by surface glycoproteins.
• Variant Specific Glycoprotein (VSG) is the major surface coat protein, with different VSG types expressed during infection waves.

Purpose of the Study:

• To investigate the structural diversity and functional implications of Variant Specific Glycoprotein (VSG) in African trypanosomes.
• To understand how VSG structure contributes to antigenic variation and host immune response modulation.

Main Methods:

• Analysis of VSG molecular weight and carbohydrate content.
• Amino acid sequence comparison to identify conserved regions (isotypy) and homology.
• Assessment of alpha-helix content using Chou-Fasman calculations and circular dichroism.
• Investigation of VSG association and C-terminal domain function.

Main Results:

• VSGs exhibit variations in molecular weight (53,000-63,000 d) and glycosylation.
• Conserved C-terminal residues (approx. 30) show isotypy, while overall homology between VSGs is low.
• Significant alpha-helical content (up to 80%) suggests diverse folding patterns.
• Lipid-associated and transmembrane forms of VSG have been identified.
• VSG structure is critical for antigenic variation and may suppress host humoral immunity.

Conclusions:

• VSG structural heterogeneity, including glycosylation and folding, is key to trypanosome survival.
• The C-terminal region plays a role in VSG structure and potentially host interactions.
• VSG's dual role in immune evasion and immune modulation highlights its importance in trypanosome pathogenesis.