5j3n
C-terminal domain of EcoR124I HsdR subunit fused with the pH-sensitive GFP variant ratiometric pHluorin
Structural highlights
FunctionT1R1_ECOLX The restriction (R) subunit of a type I restriction enzyme that recognizes 5'-GAAN(6)RTCG-3' (for EcoR124I) and 5'-GAAN(7)RTCG-3' (for EcoR124II) and cleaves a random distance away (PubMed:2784505). Subunit R is required for both nuclease and ATPase activities, but not for modification (Probable) (PubMed:12654995). After locating an unmethylated recognition site, the enzyme complex serves as a molecular motor that translocates DNA in an ATP-dependent manner until a collision occurs that triggers cleavage (PubMed:15300241). The enzyme undergoes major structural changes to bring the motor domains into contact with DNA, allowing DNA translocation. This prevents DNA access to the catalytic domains of both the R and M subunits, preventing both restriction and methylation (PubMed:32483229). The R(1)M(2)S(1) complex translocates an average of 555 bp/second on nicked DNA; the R(2)M(2)S(1) complex translocates at double that speed (PubMed:15300241). The 2 R subunit motors are independent and track along the helical pitch of the DNA, inducing positive supercoiling ahead of themselves (PubMed:15300241).[1] [2] [3] [4] [5] GFP_AEQVI Energy-transfer acceptor. Its role is to transduce the blue chemiluminescence of the protein aequorin into green fluorescent light by energy transfer. Fluoresces in vivo upon receiving energy from the Ca(2+)-activated photoprotein aequorin. Publication Abstract from PubMedAlthough EcoR124 is one of the better-studied Type I restriction-modification enzymes, it still presents many challenges to detailed analyses because of its structural and functional complexity and missing structural information. In all available structures of its motor subunit HsdR, responsible for DNA translocation and cleavage, a large part of the HsdR C terminus remains unresolved. The crystal structure of the C terminus of HsdR, obtained with a crystallization chaperone in the form of pHluorin fusion and refined to 2.45 A, revealed that this part of the protein forms an independent domain with its own hydrophobic core and displays a unique alpha-helical fold. The full-length HsdR model, based on the wild-type structure and the herein determined C-terminal domain, disclosed a proposed DNA-binding groove lined by positively charged residues. In vivo and in vitro assays with a C-terminal deletion mutant of HsdR supported the idea that this domain is involved in complex assembly and DNA binding. Conserved residues identified through sequence analysis of the C-terminal domain may play a key role in protein-protein and protein-DNA interactions. We conclude that the motor subunit of EcoR124 comprises five structural and functional domains, with the fifth, C-terminal domain revealing a unique fold characterized by four conserved motifs in the IC subfamily of Type I restriction-modification systems. In summary, structural and biochemical results reported here support a model in which the C-terminal domain of the motor subunit HsdR of the endonuclease EcoR124 is involved in complex assembly and DNA binding. Crystal structure of a novel domain of the motor subunit of the Type I restriction enzyme EcoR124 involved in complex assembly and DNA binding.,Grinkevich P, Sinha D, Iermak I, Guzanova A, Weiserova M, Ludwig J, Mesters JR, Ettrich RH J Biol Chem. 2018 Jul 27. pii: RA118.003978. doi: 10.1074/jbc.RA118.003978. PMID:30054276[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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