Cas6b

Cas6b is a member of the Cas6 family of CRISPR-associated ribonucleases. It functions as an endoribonuclease involved in the maturation of CRISPR RNAs (crRNAs) by cleaving precursor crRNA (pre-crRNA) within the repeat sequence to generate mature crRNA that guide interference complexes. Cas6b orthologs have been identified in several bacterial and archaeal species that carry Type I-B and related CRISPR-Cas systems.

Mechanism and recognition: Cas6b recognizes conserved structural motifs, such as hairpin and stem-loop structures, within the CRISPR repeat and cleaves at a defined position to produce the mature crRNA with a characteristic 5' handle that is used by downstream effector complexes.

Structure and biophysics: Cas6b proteins typically adopt a two-domain fold similar to other Cas6 proteins, with catalytic residues organized to perform endonucleolytic cleavage. Many Cas6b enzymes function without metal ions, though activity can vary among orthologs.

Biological role and interactions: After maturation, crRNA associates with Cas proteins to form a surveillance complex that recognizes complementary invader sequences. Cas6b thereby links pre-crRNA processing to the assembly of immune effector complexes in Type I-B CRISPR systems.

Evolution and naming: Cas6b is one of several Cas6 paralogs (including Cas6a and Cas6c) distributed across diverse bacteria and archaea, reflecting modular evolution of CRISPR-Cas systems.

Research and potential: Ongoing studies of Cas6b aim to elucidate crRNA processing mechanisms and the architecture of Type I-B CRISPR loci, with implications for CRISPR biology and potential biotechnological applications.