Structural Basis for Dimerization and Activation of UvrD-family Helicases

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• UvrD-family helicases are essential motor proteins involved in DNA replication, recombination, repair, and transcription.
• These enzymes translocate along single-stranded DNA as monomers but require dimerization for DNA unwinding activity.
• Previous structural studies lacked insights into the dimeric state of UvrD helicases.

Purpose of the Study:

• To determine the first structures of a dimeric UvrD-family helicase, Mycobacterium tuberculosis UvrD1.
• To elucidate the structural basis of UvrD1 activation through dimerization and DNA binding.
• To understand the regulatory role of the 2B subdomain in UvrD helicase function.

Main Methods:

• X-ray crystallography was used to obtain structures of apo UvrD1 dimer and DNA-bound UvrD1 dimer.
• Structural analysis of monomeric and dimeric forms of UvrD1, including bound to a DNA junction.
• Biochemical experiments were performed to confirm the dimerization interface in E. coli UvrD.

Main Results:

• The first structures of dimeric UvrD1, free and bound to a DNA junction, were determined.
• Dimerization occurs through the 2B subdomains, with distinct conformations in the DNA-bound state.
• Apo UvrD1 dimer exhibits symmetric compact and extended forms, indicating flexibility.
• Inactive monomeric UvrD1 shows inhibitory 2B subdomain-DNA contacts, relieved by dimerization.

Conclusions:

• Dimerization of UvrD1, mediated by 2B subdomain re-orientation, is crucial for relieving auto-inhibition and enabling DNA unwinding.
• The 2B subdomain plays a significant regulatory role in UvrD helicase function, rather than direct DNA unwinding.
• These findings provide structural insights into the activation mechanism of UvrD-family helicases.