The assembly of filamentous appendages at the surface of bacteria is essential in many infection mechanisms. The extent of mechanical, dynamical, and functional properties of such appendages is very diverse, ranging from a structural scaffold of the pathogen-host cell interaction to cell motility, surface adhesion, or the export of virulence effectors. In particular, the architectures of several bacterial secretion systems have revealed the presence of filamentous architectures, known as pili, fimbriae, andneedles. At the macroscopic level, filamentous bacterial appendages appear as thin extracellular filaments of several nanometers in diameter and up to several microns in length. The structural characterization of these appendages at atomic-scale resolution represents an extremely challenging task because of their inherent noncrystallinity and very poor solubility. Here, we describe protocols based on recent advances in solid-state NMR spectroscopy to investigate the secondary structure, subunit-subunit protein interactions, symmetry parameters, and atomic architecture of bacterial filaments.
Keywords: Helical symmetry; Needle; Pilus; Protein assembly; Protein complex; Solid-state nuclear magnetic resonance; Structure determination.