The molecular architecture of the kidney slit diaphragm

Vertebrate life depends on renal function to filter excess fluid and remove low molecular-weight waste products. An essential component of the kidney filtration barrier is the slit diaphragm (SD), a specialized cell-cell junction between podocytes. Although the constituents of the SD have recently been identified, its molecular architecture remains elusive. Here, we use cryo-electron tomography of vitreous lamellae from high-pressure frozen native murine glomeruli to analyse the molecular architecture of the SD. In our tomographic reconstructions, the “central dot” of the SD resembles a fishnet pattern. After sub-tomogram averaging and molecular dynamics flexible fitting of Nephrin and Neph1, the main constituents of the SD, an ordered crisscross arrangement can be seen. The resulting molecular model of the SD suggests at least four contact sites for each Nephrin and two contact sites for each Neph1 and renders the SD as a quasi-crystalline, sheet-like molecular polymer that is able to compensate for mechanical forces. Our architectural understanding of the murine SD reconciles previous findings and provides a mechanistic framework for the understanding of renal disease.