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bioRxiv · 10.64898/2026.05.20.726581

A Conserved Mechanism for Dimerization and Activation of Superfamily 1A UvrD-family Helicases

Nguyen, B.·Mersch, K. N.·Chadda, A.·Galburt, E.·Lohman, T. M.
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Abstract

DNA helicases are ATP-dependent motor proteins that catalyze duplex DNA unwinding and are involved in DNA repair, recombination and replication restart. Prominent members of the non-hexameric SF1A UvrD-family helicases are E. coli UvrD, Rep, B. stearothermophilus PcrA and M. tuberculosis UvrD1. SF1A monomers are processive 3 to 5 single stranded DNA translocases, but need to be activated to become DNA helicases. One mechanism of activation is dimerization. Whereas Rep, UvrD and PcrA form non-covalent dimers, the Mtb UvrD1 helicase forms a redox-dependent covalent dimer. Dimerization of Mtb UvrD1 occurs between the same regulatory domain (2B) within each subunit stabilized by a disulfide bond formed between the same cysteine (Cys451) within each subunit. Dimerization relieves an inhibitory interaction between the 2B domain and duplex DNA within the monomer-DNA complex. We show here that Rep, UvrD and PcrA dimerize using the same 2B-2B interface. By placing a Cys residue within the 2B domains of Rep, UvrD and PcrA in the structurally equivalent position occupied by Cys451 of Mtb UvrD1, all three enzymes form redox-dependent covalent dimers that are constitutively active helicases with increased processivity compared to the non-covalent dimers. Hence, the 2B domain is a general dimerization domain for UvrD-family SF1A helicases.

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Nguyen, B., Mersch, K. N., Chadda, A., Galburt, E., Lohman, T. M.. 2026-05-21. A Conserved Mechanism for Dimerization and Activation of Superfamily 1A UvrD-family Helicases. https://doi.org/10.64898/2026.05.20.726581

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