Activation of Human Meiosis-specific Recombinase Dmc1 by Ca2+

Efim I. Golub,Andrzej Stasiak,Dmitry V. Bugreev,Alicja Z. Stasiak,Alexander V. Mazin

doi:10.1074/jbc.m502248200

Abstract

Rad51 and its meiotic homolog Dmc1 are key proteins of homologous recombination in eukaryotes. These proteins form nucleoprotein complexes on single-stranded DNA that promote a search for homology and that perform DNA strand exchange, the two essential steps of genetic recombination. Previously, we demonstrated that Ca2+ greatly stimulates the DNA strand exchange activity of human (h) Rad51 protein (Bugreev, D. V., and Mazin, A. V. (2004) Proc. Natl. Acad. Sci. U. S. A. 101, 9988-9993). Here, we show that the DNA strand exchange activity of hDmc1 protein is also stimulated by Ca2+. However, the mechanism of stimulation of hDmc1 protein appears to be different from that of hRad51 protein. In the case of hRad51 protein, Ca2+ acts primarily by inhibiting its ATPase activity, thereby preventing self-conversion into an inactive ADP-bound complex. In contrast, we demonstrate that hDmc1 protein does not self-convert into a stable ADP-bound complex. The results indicate that activation of hDmc1 is mediated through conformational changes induced by free Ca2+ ion binding to a protein site that is distinct from the Mg2+.ATP-binding center. These conformational changes are manifested by formation of more stable filamentous hDmc1.single-stranded DNA complexes. Our results demonstrate a universal role of Ca2+ in stimulation of mammalian DNA strand exchange proteins and reveal diversity in the mechanisms of this stimulation.

Highlights

Rad51 and its meiotic homolog Dmc1 are key proteins of homologous recombination in eukaryotes
Ca2ϩ Stimulates the DNA Strand Exchange Activity of hDmc1 Protein—Previously, we demonstrated that Ca2ϩ strongly stimulates the DNA strand exchange activity of hRad51 protein [22]
We studied the effect of Ca2ϩ on the DNA strand exchange activity of hDmc1 protein, a meiosisspecific homolog of hRad51 protein

Summary

Introduction

Rad and its meiotic homolog Dmc are key proteins of homologous recombination in eukaryotes These proteins form nucleoprotein complexes on single-stranded DNA that promote a search for homology and that perform DNA strand exchange, the two essential steps of genetic recombination. The results indicate that activation of hDmc is mediated through conformational changes induced by free Ca2؉ ion binding to a protein site that is distinct from the Mg2؉1⁄7ATP-binding center These conformational changes are manifested by formation of more stable filamentous hDmc11⁄7single-stranded DNA complexes. It is known that both Rad and Dmc can polymerize on the ssDNA tails to form extended nucleoprotein complexes that promote a search for homologous DNA and that perform DNA strand exchange [13,14,15,16,17]. It was found that KCl at elevated concentrations (100 –200 mM) strongly stimulates the DNA strand exchange activity of hDmc protein and promotes the formation of hDmc11⁄7ssDNA helical nucleoprotein filaments [17]

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Results

Conclusion