Heterogeneity in E. coli RecBCD Helicase-DNA Binding and Base Pair Melting

•ITC studies show that RecBCD is able to melt at least 11 base pairs upon binding a DNA duplex blunt end.•Cryo-EM structures of RecBCD alone and in complex with DNA indicate significant heterogeneity.•Structural classes show the presence and absence of RecB nuclease domain is affected by DNA binding.•Structural classes show differences in the amount of DNA melted by RecBCD.•RecBCD-DNA complexes exist in equilibrium between states with different amounts of DNA melting.