Water, water, every where—the advent of hydrated pili structure

Protein structure is defined by its surrounding water. Naturally, this is also true for the gigantic protein filaments that pathogenic bacteria use to attach to and colonize their host cells. Structures of these filaments for which water can be identified with high confidence have stayed elusive for the longest time. In this issue of The FEBS Journal, Petrova et al. unveil the first fully hydrated Type I pilus structure from uropathogenic E. coli. In a powerful showcase of the current capabilities of cryo-EM, their structure beautifully visualizes internal water channels that traverse the pilus, thus marking the advent of hydrated pilus structural biology.