Despite the central role of division in bacterial physiology, how division proteins work together as a nanoscale machine to divide the cell remains poorly understood. Cell division by cell wall synthesis proteins is guided by the cytoskeleton protein FtsZ, which assembles at mid-cell as a dense Z-ring formed of treadmilling filaments. However, although FtsZ treadmilling is essential for cell division, the function of FtsZ treadmilling remains unclear. Here, we systematically resolve the function of FtsZ treadmilling across each stage of division in the Gram-positive model organism Bacillus subtilis using a combination of nanofabrication, advanced microscopy, and microfluidics to measure the division-protein dynamics in live cells with ultrahigh sensitivity. We find that FtsZ treadmilling has two essential functions: mediating condensation of diffuse FtsZ filaments into a dense Z-ring, and initiating constriction by guiding septal cell wall synthesis. After constriction initiation, FtsZ treadmilling has a dispensable function in accelerating septal constriction rate. Our results show that FtsZ treadmilling is critical for assembling and initiating the bacterial cell division machine.

Filamentous plant pathogens deliver effector proteins to host cells to promote infection. The Phytophthora infestans RXLRtype effector PexRD54 binds potato ATG8 via its ATG8 familyinteracting motif (AIM) and perturbs host-selective autophagy. However, the structural basis of this interaction remains unknown. Here, we define the crystal structure of PexRD54, which includes a modular architecture, including five tandem repeat domains, with the AIM sequence presented at the disordered C terminus. To determine the interface between PexRD54 and ATG8, we solved the crystal structure of potato ATG8CL in complex with a peptide comprising the effector's AIM sequence, and we established a model of the full-length PexRD54-ATG8CL complex using small angle x-ray scattering. Structureinformed deletion of the PexRD54 tandem domains reveals retention of ATG8CL binding in vitro and in planta. This study offers new insights into structure/function relationships of oomycete RXLR effectors and how these proteins engage with host cell targets to promote disease.During selective autophagy, specific cellular constituents can be targeted to autophagic pathways for subcellular trafficking or degradation (1-3). The autophagy toolkit includes around 40 ATG (autophagy-related) proteins. Together, they help initiate, regulate, and form the constituents of autophagic pathways. The role of selective autophagy in the response to pathogen challenge in animal cells is increasingly being appreciated and includes direct elimination of microorganisms and control of immunityrelated signaling (4, 5). In turn, microorganisms have developed mechanisms to perturb host-selective autophagy to either shut it down and promote infection (4, 5) or activate it and re-direct nutrients to the parasite (6). There is also evidence that membrane formation and trafficking, as controlled by ATG proteins, are exploited by numerous viruses (7). To date, the role of hostselective autophagy in host-microbe interactions has mostly been studied in mammals. The role of host-selective autophagy in plant-microbe interactions, and how it is manipulated by plant pathogens, remains poorly understood.ATG8 is a ubiquitin-like protein that performs multiple functions in autophagy. It is cycled, via conjugation and deconjugation reactions, to the membrane lipid phosphatidylethanolamine, and this localization is important for autophagosome biogenesis (8). The intracellular animal pathogen Legionella pneumophila targets this process by delivering type IV secreted effector protein RavZ, which irreversibly deconjugates ATG8 from membranes and restricts autophagy (9). ATG8 also functions as an adaptor to interact with proteins containing an ATG8-interacting motif (AIM).3 AIM-containing proteins can serve as receptors for cargo destined for autophagosomes. The core AIM sequence is defined as ⍀XX⌿, where ⍀ is an aromatic amino acid (Trp, Tyr, or Phe); X is any residue, and ⌿ is an aliphatic amino acid (Leu, Ile, and Val) (10 -12). Frequently, residues just to the N terminus of the ⍀XX⌿ mot...

Acute kidney injury (AKI) is an abrupt reduction in kidney function caused by different pathological processes. It is associated with a significant morbidity and mortality in the acute phase and an increased risk of developing End Stage Renal Disease. Despite the progress in the management of the disease, mortality rates in the last five decades remain unchanged at around 50%. Therefore there is an urgent need to find new therapeutic strategies to treat AKI. Lysosomal proteases, particularly Cathepsin D (CtsD), play multiple roles in apoptosis however, their role in AKI is still unknown. Here we describe a novel role for CtsD in AKI. CtsD expression was upregulated in damaged tubular cells in nephrotoxic and ischemia reperfusion (IRI) induced AKI. CtsD inhibition using Pepstatin A led to an improvement in kidney function, a reduction in apoptosis and a decrease in tubular cell damage in kidneys with nephrotoxic or IRI induced AKI. Pepstatin A treatment slowed interstitial fibrosis progression following IRI induced AKI. Renal transplant biopsies with acute tubular necrosis demonstrated high levels of CtsD in damaged tubular cells. These results support a role for CtsD in apoptosis during AKI opening new avenues for the treatment of AKI by targeting lysosomal proteases.

ABSTRACTDespite the central role of division in bacterial physiology, how division proteins work together as a nanoscale machine to divide the cell remains poorly understood. Cell division by cell wall synthesis proteins is guided by the cytoskeleton protein FtsZ, which assembles at mid-cell as a dense Z-ring formed of motile treadmilling filaments1,2. However, although FtsZ treadmilling is essential for cell division, the function of FtsZ treadmilling motility remains unclear2–5. Here, we systematically resolve the function of FtsZ treadmilling across each stage of division in the Gram-positive model organism Bacillus subtilis using a novel combination of nanofabrication, advanced microscopy, and microfluidics to measure the division-protein dynamics in live cells with ultrahigh sensitivity. We find that FtsZ treadmilling has two essential functions: mediating condensation of diffuse FtsZ filaments into a dense Z-ring, and initiating constriction by guiding septal cell wall synthesis. After constriction initiation, FtsZ treadmilling has a dispensable function in accelerating septal constriction rate. Our results show that FtsZ treadmilling is critical for assembling and initiating the bacterial cell division machine.