RecG protein

From Proteopedia

Revision as of 10:47, 29 March 2018

RecG

The RecG protein of Escherichia coli is a Superfamily 2 (SF2) branched-DNA-specific helicase which promotes rescue of damaged replication forks by catalysing their unwinding and conversion to Holliday junctions. A single RecG monomer unwinds two DNA duplexes; the leading strand duplex and the lagging strand duplex and then reanneal the parental and the newly synthetized strands. This mechanism of repair is ATP-dependent and does not require DNA double strand break. RecG works synergistically with the RuvABC repair system^[1],^[2].

SUPERFAMILY 2 HELICASES

Helicases are a ubiquitous group of enzymes that use the energy of nucleoside triphosphate (NTP) hydrolysis to catalyze the separation of double-stranded nucleic acids (dsNA). Therefore, helicases are involved in essentially every step in DNA and RNA metabolism, including replication, DNA repair, recombination, transcription, translation, chromatin rearrangement, ribosome synthesis, RNA maturation and splicing, nuclear export, Holliday junction movement, and displacement of proteins from DNA and RNA.

Superfamily 2 is the largest and most diverse of the helicase superfamilies. It has been further divided into families including RecQ-like, RecG-like, Rad3/XPD, Ski2-like, type I restriction enzyme, RIG-I-like, NS3/NPH-II, DEAH/RHA, DEAD-box, and Swi/Snf families based on sequence homology. Since SF2 helicases function in diverse parts of nucleic acid metabolism, defects are associated with a variety of diseases including predisposition to cancer, premature aging, immunodeficiency, and mental retardation^[3].

STRUCTURE

PDB access: 1GM5

Crystal structure of Thermatoga maritima RecG protein bound to three-way DNA junction has been determined at a 3.24 Å resolution. The protein complexed with ADP and synthetic DNA substrate that mimics a stalled replication fork in which the leading strand synthesis is behind that of the lagging strand. The structure of RecG revealed a monomeric conformational arrangement that can be subdivided into three domains: Domain 1 (residues 1-350), Domain 2 (residues 351–549), and Domain 3 (residues 550–780). Domain 1 is at the N terminus and is about a half of the protein. It contains a long α helix in the center of the domain. This helix provides a rigid structural foundation upon which the rest of the domain is folded. There are two common structural motifs in Domain 1. Residues 21–99 form an antiparallel four helix bundle, preceded by an additional α helix. The second one is a greek key motif (residues 154–252) that is conserved in all RecG sequences. This motif is the binding site of the protein to the DNA. The C-terminal domains: Domains 2 and 3 contain the characteristic motifs that identify RecG as an SF2 helicase. This part of the protein is structurally homologous with other SF2 helicases. ATP binds in the cleft between these domains and induces change in their relative orientation. Domain’s 3 last 50 residues are forming a hook that wraps around the extended α helix of the Domain 1. This interaction provides a link between Domains 1 and 3 that is likely to be affected by nucleotide binding^[4].

1. ↑ Singleton, M. R., Scaife, S. & Wigley, D. B. Structural analysis of DNA replication fork reversal by RecG. Cell 107, 79–89 (2001)
2. ↑ Rudolph, C. J., Upton, A. L., Briggs, G. S. & Lloyd, R. G. Is RecG a general guardian of the bacterial genome? DNA Repair 9, 210–223 (2010)
3. ↑ Byrd, A. K., & Raney, K. D. (2012). Superfamily 2 helicases. Frontiers in Bioscience (Landmark Edition), 17, 2070–2088
4. ↑ Singleton, M. R., Scaife, S. & Wigley, D. B. Structural analysis of DNA replication fork reversal by RecG. Cell 107, 79–89 (2001)