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J. Biol. Chem., Vol. 281, Issue 18, 12849-12857, May 5, 2006

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Three HRDC Domains Differentially Modulate Deinococcus radiodurans RecQ DNA Helicase Biochemical Activity^*

From the Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706-1532

RecQ helicases are key genome maintenance enzymes that function in DNA replication, recombination, and repair. In contrast to nearly every other identified RecQ family member, the RecQ helicase from the radioresistant bacterium Deinococcus radiodurans encodes three "Helicase and RNase D C-terminal" (HRDC) domains at its C terminus. HRDC domains have been implicated in structure-specific nucleic acid binding with roles in targeting RecQ proteins to particular DNA structures; however, only RecQ proteins with single HRDC domains have been examined to date. We demonstrate that the HRDC domains can be proteolytically removed from the D. radiodurans RecQ (DrRecQ) C terminus, consistent with each forming a structural domain. Using this observation as a guide, we produced a panel of recombinant DrRecQ variants lacking combinations of its HRDC domains to investigate their biochemical functions. The N-terminal-most HRDC domain is shown to be critical for high affinity DNA binding and for efficient unwinding of DNA in some contexts. In contrast, the more C-terminal HRDC domains attenuate the DNA binding affinity and DNA-dependent ATP hydrolysis rate of the enzyme and play more complex roles in structure-specific DNA unwinding. Our results indicate that the multiple DrRecQ HRDC domains have evolved to encode DNA binding and regulatory functions in the enzyme.

Received for publication, January 4, 2006 , and in revised form, March 3, 2006.

^* This work was supported in part by National Institutes of Health Grants GM068061 andGM067085 and by a Shaw Scientist grant (to J. L. K.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Fig. S1.

¹ A Cremer Scholar. Supported in part by a National Institutes of Health training grant in molecular biophysics.

² To whom correspondence should be addressed: Dept. of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, 550 Medical Science Center, 1300 University Ave., Madison, WI 53706-1532. Tel.: 608-263-1815; Fax: 608-262-5253; E-mail: jlkeck{at}wisc.edu.

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				M. P. Killoran and J. L. Keck Structure and function of the regulatory C-terminal HRDC domain from Deinococcus radiodurans RecQ Nucleic Acids Res., May 1, 2008; 36(9): 3139 - 3149. [Abstract] [Full Text] [PDF]

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