Structural and Biochemical Investigation of the Heterodimeric Murine tRNA Guanine Transglycosylase

In tRNAAsp, tRNAAsn, tRNATyr, and tRNAHis of most bacteria and eukaryotes, the anticodon wobble position may be occupied by the modified nucleoside queuosine, which affects the speed and the accuracy of translation. Since eukaryotes are not able to synthesize queuosine de novo, they have to salvage queuine the queuosine base as a micronutrient from food and or the gut microbiome. The heterodimeric Zn2 containing enzyme tRNA guanine transglycosylase TGT catalyzes the insertion of queuine into the above named tRNAs in exchange for the genetically encoded guanine. This enzyme has attracted medical interest since it was shown to be potentially useful for the treatment of multiple sclerosis. In addition, TGT inactivation via gene knockout leads to the suppressed cell proliferation and migration of certain breast cancer cells, which may render this enzyme a potential target for the design of compounds supporting breast cancer therapy. As a prerequisite to fully exploit the medical potential of eukaryotic TGT, we have determined and analyzed a number of crystal structures of the functional murine TGT with and without bound queuine. In addition, we have investigated the importance of two residues of its non catalytic subunit on dimer stability and determined the Michaelis Menten parameters of murine TGT with respect to tRNA and several natural and artificial nucleobase substrates. Ultimately, on the basis of available TGT crystal structures, we provide an entirely conclusive reaction mechanism for this enzyme, which in detail explains why the TGT catalyzed insertion of some nucleobases into tRNA occurs reversibly while that of others is irreversibl

Radiation-induced late effects in two affected individuals of the Lilo radiation accident.

Radiation exposure leads to a risk for long-term deterministic and stochastic late effects. Two individuals exposed to protracted photon radiation in the radiological accident at the Lilo Military site in Georgia in 1997 received follow-up treatment and resection of several chronic radiation ulcers in the Bundeswehr Hospital Ulm, Germany, in 2003. Multi-parameter analysis revealed that spermatogenetic arrest and serum hormone levels in both patients had recovered compared to the status in 1997. However, we observed a persistence of altered T-cell ratios, increased ICAM1 and beta1-integrin expression, and aberrant bone marrow cells and lymphocytes with significantly increased translocations 6 years after the accident. This investigation thus identified altered end points still detectable years after the accident that suggest persistent genomic damage as well as epigenetic effects in these individuals, which may be associated with an elevated risk for the development of further late effects. Our observations further suggest the development of a chronic radiation syndrome and indicate follow-up parameters in radiation victims

Large-Scale Exome-wide Association Analysis Identifies Loci for White Blood Cell Traits and Pleiotropy with Immune-Mediated Diseases

White blood cells play diverse roles in innate and adaptive immunity. Genetic association analyses of phenotypic variation in circulating white blood cell (WBC) counts from large samples of otherwise healthy individuals can provide insights into genes and biologic pathways involved in production, differentiation, or clearance of particular WBC lineages (myeloid, lymphoid) and also potentially inform the genetic basis of autoimmune, allergic, and blood diseases. We performed an exome array-based meta-analysis of total WBC and subtype counts (neutrophils, monocytes, lymphocytes, basophils, and eosinophils) in a multi-ancestry discovery and replication sample of ∼157,622 individuals from 25 studies. We identified 16 common variants (8 of which were coding variants) associated with one or more WBC traits, the majority of which are pleiotropically associated with autoimmune diseases. Based on functional annotation, these loci included genes encoding surface markers of myeloid, lymphoid, or hematopoietic stem cell differentiation (CD69, CD33, CD87), transcription factors regulating lineage specification during hematopoiesis (ASXL1, IRF8, IKZF1, JMJD1C, ETS2-PSMG1), and molecules involved in neutrophil clearance/apoptosis (C10orf54, LTA), adhesion (TNXB), or centrosome and microtubule structure/function (KIF9, TUBD1). Together with recent reports of somatic ASXL1 mutations among individuals with idiopathic cytopenias or clonal hematopoiesis of undetermined significance, the identification of a common regulatory 3′ UTR variant of ASXL1 suggests that both germline and somatic ASXL1 mutations contribute to lower blood counts in otherwise asymptomatic individuals. These association results shed light on genetic mechanisms that regulate circulating WBC counts and suggest a prominent shared genetic architecture with inflammatory and autoimmune diseases