6oes
Cryo-EM structure of mouse RAG1/2 STC complex (without NBD domain)
Structural highlights
FunctionRAG1_MOUSE Catalytic component of the RAG complex, a multiprotein complex that mediates the DNA cleavage phase during V(D)J recombination. V(D)J recombination assembles a diverse repertoire of immunoglobulin and T-cell receptor genes in developing B and T-lymphocytes through rearrangement of different V (variable), in some cases D (diversity), and J (joining) gene segments. In the RAG complex, RAG1 mediates the DNA-binding to the conserved recombination signal sequences (RSS) and catalyzes the DNA cleavage activities by introducing a double-strand break between the RSS and the adjacent coding segment. RAG2 is not a catalytic component but is required for all known catalytic activities. DNA cleavage occurs in 2 steps: a first nick is introduced in the top strand immediately upstream of the heptamer, generating a 3'-hydroxyl group that can attack the phosphodiester bond on the opposite strand in a direct transesterification reaction, thereby creating 4 DNA ends: 2 hairpin coding ends and 2 blunt, 5'-phosphorylated ends. The chromatin structure plays an essential role in the V(D)J recombination reactions and the presence of histone H3 trimethylated at 'Lys-4' (H3K4me3) stimulates both the nicking and haipinning steps. The RAG complex also plays a role in pre-B cell allelic exclusion, a process leading to expression of a single immunoglobulin heavy chain allele to enforce clonality and monospecific recognition by the B-cell antigen receptor (BCR) expressed on individual B-lymphocytes. The introduction of DNA breaks by the RAG complex on one immunoglobulin allele induces ATM-dependent repositioning of the other allele to pericentromeric heterochromatin, preventing accessibility to the RAG complex and recombination of the second allele. In addition to its endonuclease activity, RAG1 also acts as a E3 ubiquitin-protein ligase that mediates monoubiquitination of histone H3. Histone H3 monoubiquitination is required for the joining step of V(D)J recombination. Mediates polyubiquitination of KPNA1.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] Publication Abstract from PubMedThe RAG1-RAG2 recombinase (RAG) cleaves DNA to initiate V(D)J recombination, but RAG also belongs to the RNH-type transposase family. To learn how RAG-catalyzed transposition is inhibited in developing lymphocytes, we determined the structure of a DNA-strand transfer complex of mouse RAG at 3.1-A resolution. The target DNA is a T form (T for transpositional target), which contains two >80 degrees kinks towards the minor groove, only 3 bp apart. RAG2, a late evolutionary addition in V(D)J recombination, appears to enforce the sharp kinks and additional inter-segment twisting in target DNA and thus attenuates unwanted transposition. In contrast to strand transfer complexes of genuine transposases, where severe kinks occur at the integration sites of target DNA and thus prevent the reverse reaction, the sharp kink with RAG is 1 bp away from the integration site. As a result, RAG efficiently catalyzes the disintegration reaction that restores the RSS (donor) and target DNA. How mouse RAG recombinase avoids DNA transposition.,Chen X, Cui Y, Wang H, Zhou ZH, Gellert M, Yang W Nat Struct Mol Biol. 2020 Feb;27(2):127-133. doi: 10.1038/s41594-019-0366-z. Epub, 2020 Feb 3. PMID:32015553[14] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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