RESEARCH ARTICLE


Salt Modulates Oligomerization Properties of hRad51 and hRad52 Proteins



Kamakshi Balakrishnan†, Neeraja M. Krishnan†, Basuthkar J. Rao*
Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005, India.

Article Information


Identifiers and Pagination:

Year: 2009
Volume: 2
First Page: 1
Last Page: 9
Publisher Id: TOBIOJ-2-1
DOI: 10.2174/1874196700902010001

Article History:

Received Date: 21/07/2008
Revision Received Date: 10/09/2008
Acceptance Date: 02/12/2008
Electronic publication date: 21/1/2009
Collection year: 2009

© 2008 J. Rao et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Biological sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005, India; Tel: 091-22-22782606; Fax: 091-22-22804610; E-mail: bjrao@tifr.res.in† Equal Contribution


Abstract

Human Rad52 (hRad52) and Rad51 (hRad51) proteins are important components of homologous recombination machinery involved in DNA double strand break repair. hRad52 subunits oligomerize to form rings, which are further believed to stack one over another giving rise to higher order structures. Such structures bind the ends of duplex DNA to bring about DNA end joining. hRad51 exists in the native state as oligomeric rings and monomerizes to interact with the DNA. In our current study, we report disruption and solubilization of hRad52 aggregates and higher order aggregation of hRad51 molecules at high salt (KCl) concentration. Computational analysis of the crystal structure available for N-terminal 212 amino acids of hRad52 protein reveal a dense unique distribution of salt bridges, not only between adjacent but also between penultimate subunit neighbors which perhaps contribute to stabilization of hRad52 oligomeric rings. Our results suggest that disruption of inter-subunit salt bridges and thereby perturbation of interaction between individual monomers as the underlying mechanism for salt mediated monomerization of hRad52 protein. The crystal structure of Rad51 on the other hand lacks such dense salt-bridge connectivity suggesting that salt-mediated monomerization is a feature of proteins with dense salt-bridge networks. Salt brings together the hydrophobic surface residues of hRad51 in a process termed as “salting out” resulting in aggregation of hRad51 molecules. Given the functional relevance of oligomeric hRad52 and monomeric hRad51 in homologous recombination mediated repair, our findings imply that salt regulates the oligomerization status of these repair proteins, and thereby, their functions respectively.

Keywords: hRad52, hRad51, salt bridge, monomerization, aggregation, oligomers, KCl.