The Structural Proteomics unit will perform crosslinking MS to characterize the topology of the protein-protein interactome of a particular target protein or enriched cellular fraction in situ. Examples include: interactome of pulldowns with an endogenously tagged protein of interest; interactome of vesicles\cellular compartments; interactome of bacterial cells or virus\host interactions after pulldown of specific virulence factors. Crosslinking reactions can be performed on cells, on lysates or after competitive or otherwise non-denaturing (native) elution. As these experiments require careful design, the User will be granted access to preliminary acquisitions to characterise the sample and set the correct reaction conditions, or guidance to perform the optimization at their home institution. This service will be performed by our Facility Staff in collaboration with a visiting User.