Search for: All records

Abstract CRISPR–Cas adaptive immune systems capture DNA fragments from invading mobile genetic elements and integrate them into the host genome to provide a template for RNA-guided immunity¹. CRISPR systems maintain genome integrity and avoid autoimmunity by distinguishing between self and non-self, a process for which the CRISPR/Cas1–Cas2 integrase is necessary but not sufficient^2–5. In some microorganisms, the Cas4 endonuclease assists CRISPR adaptation^6,7, but many CRISPR–Cas systems lack Cas4⁸. Here we show here that an elegant alternative pathway in a type I-E system uses an internal DnaQ-like exonuclease (DEDDh) to select and process DNA for integration using the protospacer adjacent motif (PAM). The natural Cas1–Cas2/exonuclease fusion (trimmer-integrase) catalyses coordinated DNA capture, trimming and integration. Five cryo-electron microscopy structures of the CRISPR trimmer-integrase, visualized both before and during DNA integration, show how asymmetric processing generates size-defined, PAM-containing substrates. Before genome integration, the PAM sequence is released by Cas1 and cleaved by the exonuclease, marking inserted DNA as self and preventing aberrant CRISPR targeting of the host. Together, these data support a model in which CRISPR systems lacking Cas4 use fused or recruited^9,10exonucleases for faithful acquisition of new CRISPR immune sequences. 

Abstract Acute pancreatitis is a disease associated with suffering and high lethality. Although the disease mechanism is unclear, phospholipase A2 (PLA2) produced by pancreatic acinar cells is a known pathogenic trigger. Here, we show macrophage membrane-coated nanoparticles with a built-in ‘lure and kill’ mechanism (denoted ‘MΦ-NP(L&K)’) for the treatment of acute pancreatitis. MΦ-NP(L&K) are made with polymeric cores wrapped with natural macrophage membrane doped with melittin and MJ-33. The membrane incorporated melittin and MJ-33 function as a PLA2 attractant and a PLA2 inhibitor, respectively. These molecules, together with membrane lipids, work synergistically to lure and kill PLA2 enzymes. These nanoparticles can neutralize PLA2 activity in the sera of mice and human patients with acute pancreatitis in a dose-dependent manner and suppress PLA2-induced inflammatory response accordingly. In mouse models of both mild and severe acute pancreatitis, MΦ-NP(L&K) confer effective protection against disease-associated inflammation, tissue damage and lethality. Overall, this biomimetic nanotherapeutic strategy offers an anti-PLA2 treatment option that might be applicable to a wide range of PLA2-mediated inflammatory disorders.