The vast majority of cells are protected and functionalized by a dense surface layer of glycans, proteoglycans, and glycolipids. This surface represents an underexplored space in structural biology that is exceedingly challenging to recreate in vitro. Here, we investigate β-barrel protein dynamics within an asymmetric outer membrane environment, with the trimeric autotransporter Yersinia adhesin A (YadA) as an example. Magic-angle spinning NMR relaxation data and a model-free approach reveal increased mobility in the second half of strand β2 after the conserved G72, which is responsible for membrane insertion and autotransport, and in the subsequent loop toward β3. In contrast, the protomer-protomer interaction sites (β1