Two distinct archaeal type IV pili structures formed by proteins with identical sequence

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Type IV pili (T4P) are common archaeal surface appendages involved in adhesion, biofilm formation, motility, and communication.
• Understanding T4P structure is crucial for deciphering their diverse biological roles in archaea.

Purpose of the Study:

• To determine the atomic structures of two distinct adhesive T4P from Saccharolobus islandicus.
• To investigate how the same pilin polypeptide can form structurally different pili.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the atomic structures of the pili.
• Comparative analysis of T4P structures assembled under different growth conditions.

Main Results:

• Two distinct T4P structures, mono-pilus and tri-pilus, were identified, both assembled from the same pilin polypeptide.
• The tri-pilus exhibited three different pilin conformations, with outer domains rotating up to 180° compared to the mono-pilus.
• Both pilus forms utilize the same secretion system components.

Conclusions:

• Archaeal T4P structures are less constrained than archaeal flagellar filaments.
• The same secretion machinery can produce structurally diverse T4P, highlighting conformational flexibility.
• This flexibility likely contributes to the varied functions of archaeal T4P.