RecQ-like helicases, which include 5 members in the human genome, are important in maintaining genome integrity. We present a crystal structure of a truncated form of the human RECQ1 protein with Mg-ADP. The truncated protein is active in DNA fork unwinding but lacks other activities of the full-length enzyme: disruption of Holliday junctions and DNA strand annealing. The structure of human RECQ1 resembles that of Escherichia coli RecQ, with some important differences. All structural domains are conserved, including the 2 RecA-like domains and the RecQ-specific zinc-binding and winged-helix (WH) domains. However, the WH domain is positioned at a different orientation from that of the E. coli enzyme. We identify a prominent ␤-hairpin of the WH domain as essential for DNA strand separation, which may be analogous to DNA strand-separation features of other DNA helicases. This hairpin is significantly shorter in the E. coli enzyme and is not required for its helicase activity, suggesting that there are significant differences between the modes of action of RecQ family members.DNA helicase ͉ DNA repair ͉ Holliday junction ͉ structural genomics ͉ winged helix T he RecQ helicases are a family of DNA-unwinding enzymes conserved from prokaryotes to mammals that play a key role in the maintenance of genome stability. The RecQ helicase family has 5 representatives in the human genome (1-3): RECQ1 (also known as RECQL or RECQL1), BLM, WRN, RECQ4, and RECQ5. Although these 5 enzymes are similar in their catalytic core, they probably have distinct functions, as indicated by the genetic disorders associated to mutations in the genes of BLM, WRN, and RECQ4. In particular, mutations in the gene encoding for BLM (4) are associated with the Bloom's syndrome (BS), which is manifested as an increased incidence of a wide spectrum of cancers. Werner's syndrome (WS), which is linked to mutations in the WRN (5) gene, involves many signs of premature aging, as well as a predisposition to a more limited spectrum of cancers. Mutations in the gene of RECQ4 are the cause of more varied genetic disease phenotypes, including Rothmund-Thomson (RTS) (6, 7), RAPADILINO (8), and Baller-Gerold (9) syndromes. No disease phenotypes have been associated with mutations in the genes of the other 2 family members, RECQ1 and RECQ5 yet, although they may be responsible for additional cancer predisposition disorders that are distinct from RTS, BS, and WS. In this regard, interesting candidates are patients with a phenotype similar to that of RTS individuals who do not carry any mutations in the RECQ4 gene (7). A possible role of RECQ1 in genome maintenance is suggested by several observations (reviewed in ref 10). Biochemical purification from human embryonic kidney cells recovered RECQ1 as the major Holliday junction (HJ) branch migration activity (11). Knockout of the RECQ1 gene in mice (12) or suppression of its expression in HeLa cells (11) resulted in cellular phenotypes that include chromosomal instability, increased sister chromatid exchange, and hei...

Summary The risk of developing hepatocellular carcinoma (HCC) in patients with thalassaemia is increased by transfusion‐transmitted infections and haemosiderosis. All Italian Thalassaemia Centres use an ad hoc form to report all diagnoses of HCC to the Italian Registry. Since our last report, in 2002, up to December 2012, 62 new cases were identified, 52% of whom were affected by thalassaemia major (TM) and 45% by thalassaemia intermedia (TI). Two had sickle‐thalassaemia (ST). The incidence of the tumour is increasing, possibly because of the longer survival of patients and consequent longer exposure to the noxious effects of the hepatotropic viruses and iron. Three patients were hepatitis B surface antigen‐positive, 36 patients showed evidence of past infection with hepatitis B virus (HBV). Fifty‐four patients had antibodies against hepatitis C virus (HCV), 43 of whom were HCV RNA positive. Only 4 had no evidence of exposure either to HCV or HBV. The mean liver iron concentration was 8 mg/g dry weight. Therapy included chemoembolization, thermoablation with radiofrequency and surgical excision. Three patients underwent liver transplant, 21 received palliative therapy. As of December 2012, 41 patients had died. The average survival time from HCC detection to death was 11·5 months (1·4–107·2 months). Ultrasonography is recommended every 6 months to enable early diagnosis of HCC, which is crucial to decrease mortality.

RecQ helicases maintain chromosome stability by resolving a number of highly specific DNA structures that would otherwise impede the correct transmission of genetic information. Previous studies have shown that two human RecQ helicases, BLM and WRN, have very similar substrate specificities and preferentially unwind noncanonical DNA structures, such as synthetic Holliday junctions and G-quadruplex DNA. Here, we extend this analysis of BLM to include new substrates and have compared the substrate specificity of BLM with that of another human RecQ helicase, RECQ1. Our findings show that RECQ1 has a distinct substrate specificity compared with BLM. In particular, RECQ1 cannot unwind G-quadruplexes or RNA-DNA hybrid structures, even in the presence of the single-stranded binding protein, human replication protein A, that stimulates its DNA helicase activity. Moreover, RECQ1 cannot substitute for BLM in the regression of a model replication fork and is very inefficient in displacing plasmid D-loops lacking a 3-tail. Conversely, RECQ1, but not BLM, is able to resolve immobile Holliday junction structures lacking an homologous core, even in the absence of human replication protein A. Mutagenesis studies show that the N-terminal region (residues 1-56) of RECQ1 is necessary both for protein oligomerization and for this Holliday junction disruption activity. These results suggest that the N-terminal domain or the higher order oligomer formation promoted by the N terminus is essential for the ability of RECQ1 to disrupt Holliday junctions. Collectively, our findings highlight several differences between the substrate specificities of RECQ1 and BLM (and by inference WRN) and suggest that these enzymes play nonoverlapping functions in cells.

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Bone fragility has been recognized as a complication of diabetes, both type 1 diabetes (T1D) and type 2 diabetes (T2D), whereas the relationship between prediabetes and fracture risk is less clear. Fractures can deeply impact a diabetic patient’s quality of life. However, the mechanisms underlying bone fragility in diabetes are complex and have not been fully elucidated. Patients with T1D generally exhibit low bone mineral density (BMD), although the relatively small reduction in BMD does not entirely explain the increase in fracture risk. On the contrary, patients with T2D or prediabetes have normal or even higher BMD as compared with healthy subjects. These observations suggest that factors other than bone mass may influence fracture risk. Some of these factors have been identified, including disease duration, poor glycemic control, presence of diabetes complications, and certain antidiabetic drugs. Nevertheless, currently available tools for the prediction of risk inadequately capture diabetic patients at increased risk of fracture. Aim of this review is to provide a comprehensive overview of bone health and the mechanisms responsible for increased susceptibility to fracture across the spectrum of glycemic status, spanning from insulin resistance to overt forms of diabetes. The management of bone fragility in diabetic patient is also discussed.

Youth with T1D having regular nutritional counseling had a diet closer to RDIs than controls and not different cardiovascular risk factors. High saturated fatty acid intake was associated with poor blood glucose control.

DNA non-homologous end joining starts with the binding of Ku heterodimers to double strand breaks. In this work, we characterized the thermodynamics of the Ku-DNA interaction by fluorescence anisotropy of the probe-labeled DNA. We determined that the microscopic dissociation constant (k d ) for the binding of Ku to a DNA binding site of the proper length (>20 bp) ranges from 22 to 29 nM at 300 mM NaCl. The binding isotherms for DNA duplexes with two or three heterodimers were analyzed with two independent models considering the presence and absence of overlapping binding sites. This analysis demonstrated that there is no or very weak nearestneighbor cooperativity among the Ku molecules. These models can most likely be applied to study the interaction of Ku with duplexes of any length. Furthermore, our salt dependence studies indicated that electrostatic interactions play a major role in the binding of Ku to DNA and that the k d decreases ϳ60-fold as the salt concentration is lowered from 300 to 200 mM. The slope (⌫ salt ) of the plot of log k d versus log[NaCl] is 12.4 ؎ 0.1. This value is among the highest reported in the literature for a protein-DNA interaction and suggests that ϳ12 ions are released upon formation of the Ku-DNA complex. In addition, comparison of the slope values measured upon varying the type of cation and anion indicated that approximately nine cations and three anions are released from DNA and Ku, respectively, when the complex is formed.