Chemical rescue of Klebsiella aerogenes urease variants lacking the carbamylated-lysine nickel ligand

Klebsiella aerogenes urease possesses a dinuclear metallocenter in which two nickel atoms are bridged by carbamylated Lys217. To assess whether carbamate-specific chemistry is required for urease activity, site-directed mutagenesis and chemical rescue strategies were combined in efforts to place a carboxylate group at the location of this metal ligand. Urease variants with Lys217 replaced by Glu, Cys, and Ala (K217E, K217C/C319A, and K217A proteins) were purified, shown to be activated by incubation with small organic acids plus Ni(II), and structurally characterized. K217C/C319A urease possessed a second change in which Cys319 was replaced by Ala in order to facilitate efforts to chemically modify Cys217; however, this covalent modification approach did not produce active urease. Chemical rescue of the K217E, K217C/C319A, and K217A variants required 2, 2, and 10 h, respectively, to reach maximal activity levels. The highest activity generated [224 micromol of urea degraded.min-1.(mg of protein)-1, for K217C/C319A urease incubated with 500 mM formic acid and 10 mM Ni at pH 6.5] corresponded to 56% of that measured for in vitro activation of the wild-type apoprotein. While the K217E apoprotein showed minimal structural perturbations, the K217C/C319A apoprotein showed a disordering of some active site residues, and the K217A apoprotein revealed a repositioning of His219 to allow the formation of a hydrogen bond with Thr169, thus replacing the hydrogen bond between the amino group of Lys217 and Thr169 in the native enzyme. Importantly, these structures allow rationalization of the relative rates and yields of chemical rescue experiments. The crystal structures of chemically rescued K217A and K217C/C319A ureases revealed a return of the active site residues to their wild-type positions. In both cases, noncovalently bound formate was structurally equivalent to the Lys-carbamate as the bridging metallocenter ligand. We conclude that carbamate-specific chemistry is not required for urease catalysis.     

Hedgehog rehabilitation in perspective

Thousands of hedgehogs are taken into care each year, mostly injured animals or late-born young unlikely to survive hibernation. Many are returned to the wild, but until recently there was little information about their welfare, behaviour or survival after release. A review of three studies undertaken in different regions of Britain, showed that the majority of 33 released adults and juveniles adapted quickly to life in the wild despite the juveniles having been raised in captivity. They found food readily, made nests and rapidly learned their way about. They all lost weight initially but, after two three weeks, stabilised at a similar weight to wild animals. The hedgehogs which were heaviest at release lost the greatest percentage of their bodyweight, suggesting they had become overweight in captivity. The hedgehogs which were known not to have survived at least six weeks after release included three road casualties and three eaten by badgers. Although wild hedgehogs may die in the same ways, it is possible that the released hedgehogs' susceptibility to such dangers may be increased by their becoming tame during captivity. However, the high survival rate suggests that the release of rehabilitated hedgehogs back into the wild is worthwhile.     

Control of Leishmania major by a monoclonal alpha beta T cell repertoire

Little is known regarding the diversity of the host T cell response that is required to maintain immunologic control of microbial pathogens. Leishmania major persist as obligate intracellular parasites within macrophages of the mammalian host. Immunity is dependent upon activation of MHC class II-restricted T cells to an effector state capable of restricting growth and dissemination of the organisms. We generated alpha-beta Leishmania-specific (ABLE) TCR transgenic mice with MHC class II-restricted T cells that recognized an immunodominant Leishmania Ag designated LACK. Naive T cells from ABLE mice proliferated in vitro after incubation with recombinant LACK or with Leishmania-parasitized macrophages and in vivo after injection into infected mice. Infected ABLE mice controlled Leishmania infection almost as well as wild-type mice despite a drastic reduction in the T cell repertoire. ABLE mice were crossed to mice with disruption of the TCR constant region alpha gene to create animals with a single alpha beta T cell repertoire. Although mice deficient in all alpha beta T cells (TCR-C alpha 0 mice) failed to control L. major, mice with a monoclonal alpha beta T cell repertoire (ABLE TCR-C alpha 0 mice) displayed substantial control. The immune system is capable of remarkable efficiency even when constrained to recognition of a single epitope from a complex organism.     

Leptomeningeal metastasis: pathophysiology, treatment, and nursing management

PURPOSE/OBJECTIVES: To review the pathophysiology, diagnosis, and clinical treatment of leptomeningeal metastasis. DATA SOURCES: Published articles, abstracts, and book chapters. DATA SYNTHESIS: Leptomeningeal metastasis is an increasingly seen complication of cancer. Treatment is intensive and may increase survival from four to five weeks without treatment to an average of six months. Clinical management and treatment of these patients is complex and best accomplished by a multi-disciplinary healthcare team. CONCLUSIONS: Information regarding the anatomy, pathophysiology, treatment, and treatment complications can facilitate the care of patients with leptomeningeal metastasis. IMPLICATIONS FOR NURSING PRACTICE: Nursing interventions should focus on patient and family education about the disease process, side-effects of treatment, and early identification of disease progression.     

A computer simulation for teaching critical thinking skills

Telephone-based health services is a fast growing subspecialty of nursing practice. It is used in demand management and managed care organizations in a highly unregulated environment. The article presents background information and identifies the need for systematic studies of ethical implications inherent in telephone-based practice. Conclusions suggest that nurses need to become actively involved in ethical decision making related to this area of practice.     

Plasma albumin induces calcium waves in rat cortical astrocytes

At the end of the 19th century, ectopic pregnancy became a surgical procedure. A century later, one third of ectopic pregnancies are treated medically. In the meantime, early detection of ectopic pregnancy became possible due to sensitive serum hCG and progesterone combined assays with transvaginal sonography and a knowledge of risk factors. Consequently, a nonsurgical approach appears to be an attractive alternative to surgery. Expectant management is recommended with a plateau or decreasing hCG and an initial level < or = 1.000 mIU/ml in asymptomatic women. Medical treatment by local or parenteral methotrexate is recommended in patients with clear evidence of an unruptured pregnancy in based on initial hCG and progesterone level, size of hemoperitoneum, ultrasound diameter of hematosalpinx and absence of clinical pain. Laparoscopy remains the gold standard but in prospective randomized trials between medical treatment and laparoscopy, in selected patients, the non-surgical approach appears to be equivalent with a similar reproductive performance.     

Use of self-operated auditory prompts by workers with moderate mental retardation to transition independently through vocational tasks

The use of single- and multiple-word self-operated auditory prompting systems by five school-age workers with moderate mental retardation to independently transition between an ordered chain of tasks was examined in two vocational settings. The effectiveness of single- and multiple-word self-operated auditory prompts was assessed using an alternating treatment design within a multiple probe across settings. Analysis of the data revealed a significant effect on the number of independent task changes made by workers when using the single- or multiple-word auditory prompting system. When prompting systems were compared with one another, no significant differences were found in the number of independent task changes made by workers. Self-operated auditory prompts served as the stimulus control for desired behavior, they were effective for teaching workers with moderate mental retardation to manage their own task change behavior, and their use generalized across settings without additional training.