The Arg-62 Residues of the TREX1 Exonuclease Act Across the Dimer Interface Contributing to Catalysis in the Opposing Protomers

Journal of Biological Chemistry (Impact Factor: 4.57). 03/2014; 289(16). DOI: 10.1074/jbc.M114.559252
Source: PubMed


TREX1 is a 3& deoxyribonuclease that degrades single- and double-stranded DNA (ssDNA and dsDNA) to prevent inappropriate nucleic acid-mediated immune activation. More than forty different disease-causing TREX1 mutations have been identified exhibiting dominant and recessive genetic phenotypes in a spectrum of autoimmune disorders. Mutations in TREX1 at positions Asp-18 and Asp-200 to His and Asn exhibit dominant autoimmune phenotypes associated with the clinical disorders Familial Chilblain Lupus and Aicardi-Goutieres syndrome. Our previous biochemical studies showed that the TREX1 dominant autoimmune disease phenotype depends upon an intact DNA binding process coupled with dysfunctional active site chemistry. Studies here show that the TREX1 Arg-62 residues extend across the dimer interface into the active site of the opposing protomer to coordinate substrate DNA and to affect catalysis in the opposing protomer. The TREX1R62A/R62A homodimer exhibits approximately 50-fold reduced ssDNA and dsDNA degradation activities relative to TREX1WT. The TREX1 D18H, D18N, D200H, and D200N dominant mutant enzymes were prepared as compound heterodimers with the TREX1 R62A substitution in the opposing protomer. The TREX1D18H/R62A, TREX1D18N/R62A, TREX1D200H/R62A, and TREX1D200N/R62A compound heterodimers exhibit higher levels of ss- and dsDNA degradation activities than the homodimers demonstrating the requirement for TREX1 Arg-62 residues to provide necessary structural elements for full catalytic activity in the opposing TREX1 protomer. This concept is further supported by the loss of dominant negative effects in the TREX1 D18H, D18N, D200H, and D200N compound heterodimers. These data provide compelling evidence for the required TREX1 dimeric structure for full catalytic function.

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    ABSTRACT: Considering that it is a single exon gene encoding a 314 amino acid protein, the genotype-phenotype landscape of TREX1 is remarkably complex. Here we briefly describe the human diseases so-far associated with mutations in TREX1, which include Aicardi-Goutières syndrome, familial chilblain lupus, systemic lupus erythematosus and retinal vasculopathy with cerebral leukodystrophy.
    Journal of Clinical Immunology 03/2015; DOI:10.1007/s10875-015-0147-3 · 3.18 Impact Factor
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    ABSTRACT: The TREX1 gene encodes a potent DNA exonuclease, and mutations in TREX1 cause a spectrum of lupus-like autoimmune diseases. Most lupus patients develop autoantibodies to double-stranded DNA (dsDNA), but the source of DNA antigen is unknown. The TREX1 D18N mutation causes amonogenic, cutaneous form of lupus called familial chilblain lupus, and the TREX1 D18N enzyme exhibits dysfunctional dsDNA-degrading activity, providing a link between dsDNA degradation and nucleic acid-mediated autoimmune disease. We determined the structure of the TREX1 D18N protein in complex with dsDNA, revealing how this exonuclease uses a novel DNA-unwinding mechanism to separate the polynucleotide strands for single-stranded DNA (ssDNA) loading into the active site. The TREX1 D18N dsDNA interactions coupled with catalytic deficiency explain how this mutant nuclease prevents dsDNA degradation. We tested the effects of TREX1 D18N in vivo by replacing the TREX1 WT gene in mice with the TREX1 D18N allele. The TREX1 D18N mice exhibit systemic inflammation, lymphoid hyperplasia, vasculitis, and kidney disease. The observed lupus-like inflammatory disease is associated with immune activation, production of autoantibodies to dsDNA, and deposition of immune complexes in the kidney. Thus, dysfunctional dsDNA degradation by TREX1 D18N induces disease in mice that recapitulates many characteristics of human lupus. Failure to clear DNA has long been linked to lupus in humans, and these data point to dsDNA as a key substrate for TREX1 and a major antigen source in mice with dysfunctional TREX1 enzyme.
    Proceedings of the National Academy of Sciences 04/2015; 112(16):201423804. DOI:10.1073/pnas.1423804112 · 9.67 Impact Factor


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