Structural basis of self-assembly in the lipid-binding domain of mycobacterial polar growth factor Wag31

• Main Authors: Komal Choukate, Barnali Chaudhuri
• Format: Article
• Language: English
• Published: International Union of Crystallography 2020-07-01
• Series: IUCrJ
• Subjects: mycobacterial polar growth; dimer assembly; mycobacterium tuberculosis; coiled coil; lipids; filaments
• Online Access: http://scripts.iucr.org/cgi-bin/paper?S2052252520006053

Wag31, or DivIVA, is an essential protein and a drug target in the 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 enzymes at the pole for exclusive polar growth. The crystal structure of the N-terminal lipid-binding domain of mycobacterial Wag31 was determined at 2.3 Å resolution. The structure revealed a highly polar surface lined with several conserved charged residues that suggest probable sites for interactions with membrane lipids. Crystal-packing analysis revealed a previously unseen `dimer-of-dimers' assembly state of N-terminal Wag31, which is formed by antiparallel stacking of two coiled-coil dimers. Size-exclusion column-chromatography-coupled small-angle solution X-ray scattering data revealed a tetrameric form as a major assembly state of N-terminal Wag31 in solution, further supporting the crystal structure. The results suggest that, in addition to lipid binding, the N-terminal Wag31 can participate in self-assembly to form filamentous structures. Plausible models of linear self-assembly and branching of Wag31 filaments consistent with available data are suggested.