Periplasmic and fimbrial SefA from Salmonella enteritidis

Area of Science:

• Microbiology
• Structural Biology
• Protein Biochemistry

Background:

• Salmonella enteritidis fimbriae are thin, filamentous structures.
• These fimbriae are primarily composed of the fimbrin subunit SefA.
• The solubility and assembly properties of SefA were not well understood.

Purpose of the Study:

• To investigate the solubility and structural properties of SefA fimbrins.
• To understand the assembly mechanism of Salmonella enteritidis fimbriae.
• To compare the properties of assembled fimbrial SefA with unassembled periplasmic SefA.

Main Methods:

• Solubility assays at different pH and detergent conditions.
• Mass spectrometry for precise mass measurements.
• Monoclonal antibody binding and surface hydrophobicity analysis.
• Chemical cross-linking to study multimerization.

Main Results:

• Fimbrial SefA is insoluble but soluble at pH 10.5, depolymerizing in SDS.
• Periplasmic SefA is soluble and exists as monomers or dimers.
• Fimbrial and periplasmic SefA exhibit different antibody reactivity and hydrophobicity.
• Mass spectrometry confirmed no post-translational modifications.
• SefA multimerization appears to occur via N-termini, involving conformational changes before fiber assembly.
• Hydrophobic interactions maintain subunit contact within fimbriae.

Conclusions:

• SefA fimbrins undergo conformational changes and N-terminal multimerization prior to fiber assembly.
• Strong hydrophobic interactions are crucial for maintaining subunit contact in Salmonella fimbriae.
• Distinct properties of assembled vs. unassembled SefA highlight conformational changes during fimbriogenesis.