How IscB and Its Variants Recognize Single-Stranded Genetic Material

Four cryo-EM structures of IscB reveal its interaction with single-stranded nucleic acids.

• IscB forms a 10-nucleotide seed duplex with single-stranded nucleic acids, suggesting a specific initial binding mechanism.
• An alternatively positioned HNH nuclease prevents further base-pairing, acting as a conformational roadblock.
• In this intermediate state, neither the HNH nor RuvC domains can cleave the target due to obstructions.
• Full duplex formation allows additional base pairs to dislodge the HNH roadblock, exposing the RuvC active site for cleavage.
• Mutations that enhance single-stranded nucleic acid binding or relieve the conformational checkpoint may improve IscB's RNA-targeting efficiency.

Simplified