Many cellular processes rely on multi-functional molecular nanomachines, such as the ribosome (protein synthesis), bacterial pili and needles (host-pathogen interaction) or flagella (cell motion). These machines are built by the assembly of multiple copies of protein subunits into large macromolecular structures, also called supramolecular assemblies. Understanding assembly, structure and functions of these machines is hampered by the challenging structural characterization task. Indeed, these insoluble and non-crystalline objects are not amenable to high-resolution X-ray crystallography or solution NMR. Solid-state NMR (SSNMR) can provide atomic details about structure and dynamics of biological assemblies. Notably, the first atomic models of a prion in its fibrillar form (the prion domain of HET-s, see Wasmer et al., Science 2008) and a bacterial filament (the Type III Secretion System needle, see Loquet et al., Nature 2012) were established on the basis of SSNMR restraints.The Type II Secretion System (T2SS) is a complex machinery found in Gram-negative bacteria, designed to transport effector proteins from the bacterial periplasm to the extracellular space. T2SSs contain a periplasmic filament, called the pseudopilus, that organizes the secretion of the T2SS exoenzyme through the outer membrane. The pseudopilus is built by multiple copies of a single polypeptide subunit, forming an insoluble and non-crystalline macromolecular assembly. In this project, I propose to use SSNMR to solve the structure of the T2SS pseudopilus in its relevant assembled state, as well as to shed light on the specific interactions with its exoenzyme.