The crystal structure of MreC provides insights into polymer formation.

MreC is a scaffold protein required for cell shape determination through interactions with proteins related to cell wall synthesis. Here, we determined the crystal structure of the major periplasmic part of MreC from Escherichia coli at 2.1 Å resolution. The periplasmic part of MreC contains a coiled-coil domain and two six-stranded barrel domains. The coiled-coil domain is essential for dimer formation, and the two monomers are prone to relative motion that is related to the small interface of β-barrel domains. In addition, MreC forms an antiparallel filament-like structure along the coiled-coil direction, which is different from the helical array structure in Pseudomonas aeruginosa. Our structure deepens our understanding of polymer formation of MreC.