Crystal structure of RlmAI: implications for understanding the 23S rRNA G745/G748-methylation at the macrolide antibiotic-binding site

The RlmA class of enzymes (RlmA(I) and RlmA(II)) catalyzes N1-methylation of a guanine base (G745 in Gram-negative and G748 in Gram-positive bacteria) of hairpin 35 of 23S rRNA. We have determined the crystal structure of Escherichia coli RlmA(I) at 2.8-A resolution, providing 3D structure information for the RlmA class of RNA methyltransferases. The dimeric protein structure exhibits features that provide new insights into its molecular function. Each RlmA(I) molecule has a Zn-binding domain, responsible for specific recognition and binding of its rRNA substrate, and a methyltransferase domain. The asymmetric RlmA(I) dimer observed in the crystal structure has a well defined W-shaped RNA-binding cleft. Two S-adenosyl-l-methionine substrate molecules are located at the two valleys of the W-shaped RNA-binding cleft. The unique shape of the RNA-binding cleft, different from that of known RNA-binding proteins, is highly specific and structurally complements the 3D structure of hairpin 35 of bacterial 23S rRNA. Apart from the hairpin 35, parts of hairpins 33 and 34 also interact with the RlmA(I) dimer.     

Diets and cardiovascular disease: an evidence-based assessment

With rising obesity, despite low-fat diet recommendations, there is an increased interest in weight loss and alternative dietary approaches for cardiovascular health. Physicians must have an understanding of the literature to better counsel their patients about diets and cardiovascular disease. This review examines several dietary approaches to cardiovascular health and evaluates the available scientific evidence regarding these diets.     

Attained adult height in juvenile rheumatoid arthritis with or without corticosteroid treatment

Growth impairment has been described in patients with juvenile rheumatoid arthritis (JRA). Both the direct action of underlying disease and prolonged corticosteroid usage for disease management may contribute to growth impairment. The purpose of this retrospective study was to evaluate the effect of systemic corticosteroid treatment on attained adult height in patients with JRA. We reviewed patients who first visited our hospital from 1973 to 1995 with a diagnosis of JRA. Adult height (AH) and the reported parental heights of these patients were recorded. Target height (TH) is estimated according to midparental height. Patients who never had or had only transient (less than 1 week) systemic corticosteroid therapy were classified as group 1. Group 2 included patients who had corticosteroid therapy for more than 1 week but never continuously for more than 12 months, and group 3 included patients on long-term steroid treatment (continuously for more than 1 year). Height data were analysed using adult height and the difference between adult height and target height (AH minus TH). Thirty-three patients fulfilling the diagnostic criteria for JRA were reviewed. Fourteen belonged to group 1, 13 to group 2 and six to group 3. The difference between adult height and target height in group 1 was 2.96 ± 4.54 cm, in group 2 0.71 ± 6.08 cm (group 1 vs. group 2, P = 0.28), and in group 3 −11.65 ± 10.71 cm (group 1 vs. group 3, P<0.05). In 15 patients who never received corticosteroid therapy continuously for more than 1 year, AH–TH was statistically correlated neither with the cumulative corticosteroid exposure dose nor with cumulative corticosteroid exposure period by linear regression (P= 0.408, P= 0.278, respectively). We concluded that continuous systemic corticosteroid usage for less than 1 year does not affect attained adult height in JRA patients; however, prolonged corticosteroid treatment for more than 1 year can lead to irreversible growth impairment. Received: 23 May 2001 / Accepted: 11 February 2002     

Genetic mapping of ASIC4 and contrasting phenotype to ASIC1a in modulating innate fear and anxiety

Although ASIC4 is a member of the acid‐sensing ion channel (ASIC) family, we have limited knowledge of its expression and physiological function in vivo. To trace the expression of this ion channel, we generated the ASIC4‐knockout/CreERT²‐knockin (Asic4^CreERT2) mouse line. After tamoxifen induction in the Asic4^CreERT2::CAG‐STOP^floxed‐Td‐tomato double transgenic mice, we mapped the expression of ASIC4 at the cellular level in the central nervous system (CNS). ASIC4 was expressed in many brain regions, including the olfactory bulb, cerebral cortex, striatum, hippocampus, amygdala, thalamus, hypothalamus, brain stem, cerebellum, spinal cord and pituitary gland. Colocalisation studies further revealed that ASIC4 was expressed mainly in three types of cells in the CNS: (i) calretinin (CR)‐positive and/or vasoactive intestine peptide (VIP)‐positive interneurons; (ii) neural/glial antigen 2 (NG2)‐positive glia, also known as oligodendrocyte precursor cells; and (iii) cerebellar granule cells. To probe the possible role of ASIC4, we hypothesised that ASIC4 could modulate the membrane expression of ASIC1a and thus ASIC1a signaling in vivo. We conducted behavioral phenotyping of Asic4^CreERT2 mice by screening many of the known behavioral phenotypes found in Asic1a knockouts and found ASIC4 not involved in shock‐evoked fear learning and memory, seizure termination or psychostimulant‐induced locomotion/rewarding effects. In contrast, ASIC4 might play an important role in modulating the innate fear response to predator odor and anxious state because ASIC4‐mutant mice showed increased freezing response to 2,4,5‐trimethylthiazoline and elevated anxiety‐like behavior in both the open‐field and elevated‐plus maze. ASIC4 may modulate fear and anxiety by counteracting ASIC1a activity in the brain.     

Characterization of Platinum Nanoparticles Deposited on Functionalized Graphene Sheets

Due to its special electronic and ballistic transport properties, graphene has attracted much interest from researchers. In this study, platinum (Pt) nanoparticles were deposited on oxidized graphene sheets (cG). The graphene sheets were applied to overcome the corrosion problems of carbon black at operating conditions of proton exchange membrane fuel cells. To enhance the interfacial interactions between the graphene sheets and the Pt nanoparticles, the oxygen-containing functional groups were introduced onto the surface of graphene sheets. The results showed the Pt nanoparticles were uniformly dispersed on the surface of graphene sheets with a mean Pt particle size of 2.08 nm. The Pt nanoparticles deposited on graphene sheets exhibited better crystallinity and higher oxygen resistance. The metal Pt was the predominant Pt chemical state on Pt/cG (60.4%). The results from the cyclic voltammetry analysis showed the value of the electrochemical surface area (ECSA) was 88 m²/g (Pt/cG), much higher than that of Pt/C (46 m²/g). The long-term test illustrated the degradation in ECSA exhibited the order of Pt/C (33%) > Pt/cG (7%). The values of the utilization efficiency were calculated to be 64% for Pt/cG and 32% for Pt/C.