A Unique Gene Module in Thermococcales Archaea Centered on a Hypervariable Protein Containing Immunoglobulin Domains

Area of Science:

• Microbiology
• Genomics
• Archaea Biology

Background:

• Molecular mechanisms of biological conflicts and self vs. non-self recognition in archaea are not well understood.
• Immunoglobulin (Ig) domain proteins are present in archaea, but their roles in these processes are unclear.

Purpose of the Study:

• To identify and characterize novel gene modules involved in biological conflicts and recognition in archaea.
• To investigate the evolutionary and functional significance of hypervariable gene systems in Thermococcales.

Main Methods:

• Phylogenomic analysis was employed to identify widespread gene modules within Thermococcales.
• Sequence analysis was used to determine the hypervariable nature and domain composition of identified loci.

Main Results:

• A widespread, hypervariable gene module, termed VARTIG (VARiable Thermococcales IG), was identified in Thermococcales.
• VARTIG loci comprise a large Ig domain-containing protein and unique downstream genes, with hypervariability arising from recombination.
• VARTIG organization resembles Polymorphic Toxin Systems (PTS), and archaea outside Thermococcales lack VARTIG counterparts.

Conclusions:

• The VARTIG system represents a novel archaeal gene module with potential roles in inter-microbial conflicts.
• Hypotheses suggest VARTIG involvement in innate immunity or self vs. non-self discrimination, analogous to vertebrate systems.
• The analogies to vertebrate immune systems warrant further investigation into VARTIG functions.