Kinase Family RAD51B

Kinase Classification: Group SAPPK: Family RAD51B

RAD51B (RAD51L1) is a homolog of the RAD51 DNA repair protein with a single report of protein kinase activity.

Domain Structure

RAD51B consists mostly of a P-loop NTPase domain. These domains can bind ATP and are often used in proteins that hydrolyze ATP.

Evolution

RAD51B is part of the RAD51 family, with seven homologs in humans (RAD51, RAD51C-D, XRCC2-3, DMC1). Specific orthologs of RAD51B are found in all vertebrates, in Nematostella, and in algae and land plants, but not in insects, nematodes, fungi or most other basal lineages.

Protein Kinase Activity

A single report [1] shows protein kinase activity in RAD51B, and takes several steps to show that the activity is not an artefact. Human RAD51B was affinity purified as a His-tagged protein from either bacculovirus or E. coli. Th bacculovirus protein ran as a single silver-stained band, while the E. coli form was a single band by Coomassie staining. Both proteins could phosphorylate MBP and kemptide in vitro. The reaction was saturable and assayed at 0.2 pmol of phosphate incorporated into kemptide in 30 min/pmol of RAD51B. Further validation used gel-purified renatured protein and protein purified by immnoprecipitation with multiple antibodies. RAD51B was also shown to bind to and to phosphorylate p53, and probably Cyclin E, in vitro. A p53-interaction was supported by the finding that the early embryonic lethality of a RAD51B knockout could be partially rescued by a p53 knockout [2]. Kinase activity was strongly inhibitied by a K114E mutation, which was predicted to disrupt ATP binding to the A-box. No other RAD51 family member has been reported to have protein kinase activity, though all contain P-loop NTPase domains and have some potential to be kinases.

Function

The RAD51 family functions in DNA repair and homologous recombination. RAD51/RecA forms long filaments on DNA, and the other family members can also oligomerize with RAD51. RAD51B can specifically bind to RAD51C, which in turn can bind to several other family members. RAD51B overexpression of this gene was found to cause cell cycle G1 delay and cell apoptosis, which suggested a role in sensing DNA damage [3]. A chicken cell line null for RAD51B showed defects in homologous recombination and DNA repair [4]. Mutations in Arabidopsis RAD51B also showed hypersensitivity to double-stranded breaks but were otherwise viable and fertile [5].

References

1. Havre PA, Rice M, Ramos R, and Kmiec EB. HsRec2/Rad51L1, a protein influencing cell cycle progression, has protein kinase activity. Exp Cell Res. 2000 Jan 10;254(1):33-44. DOI:10.1006/excr.1999.4725 |
2. Shu Z, Smith S, Wang L, Rice MC, and Kmiec EB. Disruption of muREC2/RAD51L1 in mice results in early embryonic lethality which can Be partially rescued in a p53(-/-) background. Mol Cell Biol. 1999 Dec;19(12):8686-93. DOI:10.1128/MCB.19.12.8686 |
3. Havre PA, Rice MC, Noe M, and Kmiec EB. The human REC2/RAD51B gene acts as a DNA damage sensor by inducing G1 delay and hypersensitivity to ultraviolet irradiation. Cancer Res. 1998 Oct 15;58(20):4733-9.
4. Takata M, Sasaki MS, Sonoda E, Fukushima T, Morrison C, Albala JS, Swagemakers SM, Kanaar R, Thompson LH, and Takeda S. The Rad51 paralog Rad51B promotes homologous recombinational repair. Mol Cell Biol. 2000 Sep;20(17):6476-82. DOI:10.1128/MCB.20.17.6476-6482.2000 |
5. Osakabe K, Abe K, Yamanouchi H, Takyuu T, Yoshioka T, Ito Y, Kato T, Tabata S, Kurei S, Yoshioka Y, Machida Y, Seki M, Kobayashi M, Shinozaki K, Ichikawa H, and Toki S. Arabidopsis Rad51B is important for double-strand DNA breaks repair in somatic cells. Plant Mol Biol. 2005 Apr;57(6):819-33. DOI:10.1007/s11103-005-2187-1 |