Cryo-EM structure of the human uromodulin filament core: a unique assembly mechanism

Homopolymeric filaments of uromodulin promote pathogen clearance in urinary tract infections. A recent "eLife" paper by Stanisich et al. (IMBB) unveils an unexpected filament architecture, indicating that UMOD assembly is synchronized with proteolytic release of precursors from the membrane.

03.09.2020

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Graphical abstract Glockshuber paper — Architecture and assembly of UMOD filaments. Top: Structure of the helical UMOD filament core. Bottom: Simplest conceivable model of UMOD subunit incorporation and specific release of GPI anchored pro-UMOD by the protease hepsin (scissors).

Uromodulin (UMOD), the most abundant glycoprotein in human urine, has a multitude of roles in the urinary tract: from maintaining the water impermeable layer, inhibiting kidney stone formation, and regulating salt transport to protecting against urinary tract infections caused by various uropathogens.

Recent cryo-electron tomographic studies revealed the general architecture of the UMOD filament (Science 369, 1005-1010, 2020). Arranged in a repetitive helical pattern that resembles a fishbone, UMOD monomers come together to form long filaments that can encapsulate uropathogens by interactions between UMOD glycans and adhesive pili of pathogens.

To better understand UMOD architecture and filament formation, the core structure of the UMOD filament has now been determined at near atomic resolution using single particle cryo-EM. The 3.5 Å reconstruction was solved by the Glockshuber group (IMBB) in collaboration with the newly formed ETH Cryo-EM Knowledge Hub (CEMK; https://cemk.ethz.ch/).

The structure shows that the filament core is formed by the two C-terminal ZP subdomains of UMOD. The ZP subdomains in each monomer are separated by a ~100 Å long linker that interacts by β-sheet complementation with a ZP subdomain from a preceding and following monomer, yielding a tightly connected, helical homopolymer. The newly discovered architecture suggests a simple model of filament assembly, in which subunit incorporation is coordinated with proteolytic release of GPI-anchored UMOD precursors from the cell membrane. The mechanism may be representative for the assembly of multiple filamentous protein complexes with C-terminal ZP modules.

Link to the paper in external page "eLife".