[A protein with missing information about its tertiary structure folds into the compact globular structure]

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Yersinia pestis is a Gram-negative bacterium.
• Pili-like fibrils are important virulence factors in Yersinia pestis.
• Cafl (Cafl 13.149) is a structural protein fragment found in these fibrils.

Purpose of the Study:

• To investigate the structural properties and self-assembly capabilities of the Cafl (Cafl 13.149) fragment.
• To determine if the Cafl fragment can form a ternary structure independently.
• To understand the role of the "sticky" Alal-Thr12 segment in protein folding.

Main Methods:

• Hydrodynamic methods were employed.
• Equilibrium ultracentrifugation was used to assess the monomeric state.
• Velocity sedimentation analyzed quaternary structure.
• Intrinsic viscosity measured protein conformation and interactions.

Main Results:

• The Cafl (Cafl 13.149) fragment exists in a monomeric state.
• The fragment spontaneously forms a compact ternary structure.
• This self-assembly occurs without the need for chaperone proteins or additional subunits.
• The "sticky" Alal-Thr12 segment plays a crucial role in ternary structure formation by interacting with the acceptor cleft and hydrophobic core.

Conclusions:

• The Cafl fragment possesses intrinsic properties enabling spontaneous, ordered self-assembly into a ternary structure.
• The "sticky" segment is essential for stabilizing the ternary structure, even when sourced from a neighboring subunit.
• Understanding this self-assembly mechanism provides insights into bacterial fibril formation and protein folding.