CRISPR-associated protein 9 (Cas9) (Cas9)

CRISPR-associated protein 9 (Cas9) is a dual RNA-guided DNA endonuclease that serves as the effector protein in the Type II CRISPR-Cas bacterial adaptive immune system (UniProt: Q99ZW2). It functions by forming a ribonucleoprotein (RNP) complex with a guide RNA (gRNA) that directs the enzyme to a specific 20-nucleotide genomic sequence adjacent to a protospacer adjacent motif (PAM) (Jinek et al., 2012, Science). Upon binding, Cas9 undergoes a conformational change and utilizes its HNH and RuvC nuclease domains to induce a double-strand break (DSB) in the target DNA. In therapeutic applications, this mechanism is harnessed to modify the human genome by either disrupting a disease-causing gene through non-homologous end joining (NHEJ) or correcting a mutation via homology-directed repair (HDR) (Doudna & Charpentier, 2014, Science). The first FDA-approved therapy utilizing Cas9, exagamglogene autotemcel, targets the BCL11A enhancer to treat sickle cell disease and beta-thalassemia (FDA, 2023). Ongoing clinical development focuses on in vivo delivery for conditions like transthyretin amyloidosis and hereditary angioedema, though challenges remain regarding off-target effects and potential immune reactions to the bacterial protein (Gillmore et al., 2021, NEJM).

Other names

Csn1Cas9 nucleaseRNA-guided DNA endonuclease Cas9SpCas9CRISPR-associated endonuclease Cas9

RNA-guided site-specific DNA double-strand break induction followed by cellular DNA repair mechanisms, such as Non-Homologous End Joining (NHEJ) or Homology-Directed Repair (HDR), to achieve gene knockout, insertion, or correction.