The compact CasPi (Cas12l) bracelet "provides" a unique structural platform for DNA manipulation

CRISPR-Cas modules serve as the adaptive nucleic-acid immune systems for prokaryotes, and provide versatile tools for nucleic-acid manipulation in various organisms. Here, we discovered a new miniature type V system, CRISPR-Cas{pi} (Cas12l) ([~]860 aa), from the environmental metagenome. Complexed with a large guide-RNA ([~]170 nt) comprising the tracrRNA and crRNA, Cas{pi} (Cas12l) recognizes a unique 5 C-rich PAM for DNA cleavage under a broad range of biochemical conditions, and generates gene editing in mammalian cells. Cryo-EM study reveals a bracelet architecture of Cas{pi} effector encircling the DNA target at 3.4-[A] resolution, substantially different from the canonical two-lobe architectures of Cas12 and Cas9 nucleases. And the large guide-RNA serves as a two-arm scaffold for effector assembly. Our study expands the knowledge of DNA targeting mechanisms by CRISPR effectors, and offers an efficient but compact platform for DNA manipulations.