Crystal structure of the membrane anchoring domain of mycobacterial Wag31: a dimer-of-dimer suggests how a Wag31 filament might self-assemble

Wag31, or DivIVA, is an essential protein and a drug target in human pathogen Mycobacterium tuberculosis that self-assembles at the negatively curved membrane surface to form a higher-order structural scaffold, maintains rod-shaped cellular morphology, and localizes key cell-wall synthesizing proteins at the pole for exclusive polar growth. We determined the crystal structure of N-terminal membrane anchoring domain of mycobacterial Wag31 at 2.3 [A] resolution using molecular replacement method. Crystal packing analysis revealed a previously unseen dimer-of-dimer assembly state of N-terminal Wag31 with C2 point group symmetry, which is formed by antiparallel stacking of two coiled coil dimers. Size-exclusion column chromatography-coupled small angle solution X-ray scattering data showed a tetrameric form as a major assembly state of N-terminal Wag31 in solution, further supporting the crystal structure. Plausible models of linear self-assembling, and branching, of Wag31 filaments consistent with available data are suggested.