Computational design of the temperature optimum of an enzyme reaction

Cold-adapted enzymes are characterized both by a higher catalytic activity at low temperatures and by having their temperature optimum down-shifted, compared to mesophilic orthologs. In several cases, the optimum does not coincide with the onset of protein melting but reflects some other type of inactivation. In the psychrophilic α-amylase from an Antarctic bacterium, the inactivation is thought to originate from a specific enzyme-substrate interaction that breaks around room temperature. Here, we report a computational redesign of this enzyme aimed at shifting its temperature optimum upward. A set of mutations designed to stabilize the enzyme-substrate interaction were predicted by computer simulations of the catalytic reaction at different temperatures. The predictions were verified by kinetic experiments and crystal structures of the redesigned α-amylase, showing that the temperature optimum is indeed markedly shifted upward and that the critical surface loop controlling the temperature dependence approaches the target conformation observed in a mesophilic ortholog.

Conformational tuning improves the stability of spirocyclic nitroxides with long paramagnetic relaxation times

Nitroxides are widely used as probes and polarization transfer agents in spectroscopy and imaging. These applications require high stability towards reducing biological environments, as well as beneficial relaxation properties. While the latter is provided by spirocyclic groups on the nitroxide scaffold, such systems are not in themselves robust under reducing conditions. In this work, we introduce a strategy for stability enhancement through conformational tuning, where incorporating additional substituents on the nitroxide ring effects a shift towards highly stable closed spirocyclic conformations, as indicated by X-ray crystallography and density functional theory (DFT) calculations. Closed spirocyclohexyl nitroxides exhibit dramatically improved stability towards reduction by ascorbate, while maintaining long relaxation times in electron paramagnetic resonance (EPR) spectroscopy. These findings have important implications for the future design of new nitroxide-based spin labels and imaging agents.

Structure and Mechanism of a Cold-Adapted Bacterial Lipase

The structural origin of enzyme cold-adaptation has been the subject of considerable research efforts in recent years. Comparative studies of orthologous mesophilic-psychrophilic enzyme pairs found in nature are an obvious strategy for solving this problem, but they often suffer from relatively low sequence identity of the enzyme pairs. Small bacterial lipases adapted to distinctly different temperatures appear to provide an excellent model system for these types of studies, as they may show a very high degree of sequence conservation. Here, we report the first crystal structures of lipase A from the psychrophilic bacterium Bacillus pumilus, which confirm the high structural similarity to the mesophilic Bacillus subtilis enzyme, as indicated by their 81% sequence identity. We further employ extensive QM/MM calculations to delineate the catalytic reaction path and its energetics. The computational prediction of a rate-limiting deacylation step of the enzymatic ester hydrolysis reaction is verified by stopped-flow experiments, and steady-state kinetics confirms the psychrophilic nature of the B. pumilus enzyme. These results provide a useful benchmark for examining the structural basis of cold-adaptation and should now make it possible to disentangle the effects of the 34 mutations between the two enzymes on catalytic properties and thermal stability.

Side-Chain Interactions in d/l Peptide Nanotubes: Studies by Crystallography, NMR Spectroscopy and Molecular Dynamics

Our understanding of the factors affecting the stability of cyclic d/l peptide (CP) nanotubes remains underdeveloped. In this work, we investigate the impact of side chain alignment, hydrophobicity and charge on CP nanotube stability through X-ray crystallography, NMR spectroscopy and molecular dynamics (MD) simulations. We characterise the distinct CP-CP alignments that can form and identify stable and unstable dimers by MD simulation. We measure H-bond half-lives of synthesised CPs by ¹ H-D exchange experiments and find good correlation with predicted CP-CP stabilities. We find that hydrophobic amino acids improve CP dimer stability but experimentally reduce solubility. Charged amino acids either increase or decrease CP dimer stability depending on the relative orientation and composition of charged groups. X-ray crystal structures are solved for two CPs, revealing non-tubular folded conformations. Ultimately, this work will assist the educated design of stable tubular structures for potential applications in biomedicine.

[The role of tumor marker CA 125 in the treatment of ovarian cancer]

Among the gynaecological malignancies in Denmark, ovarian cancer still has the highest mortality. At diagnosis, the majority of the patients show disseminated diseases and are treated with a combination of surgery and chemotherapy. At the conclusion of treatment and at later control examinations, the patients are evaluated by pelvic examination, ultrasound scans, CT-scanning, determination of the tumor-marker CA 125 and explorative laparotomy ("second look operation"). Based on studies of the literature the utility of CA 125 as a marker for the activity of the disease in patients with ovarian cancer during and after treatment is evaluated. It is concluded that CA 125 levels above 35 E/ml are seen in 85% of women with ovarian cancer. CA 125 as a sole parameter cannot be used for the screening of women for ovarian cancer, since high CA 125 values may be seen in conditions other than ovarian cancer. Normalisation of CA 125 values is a condition but not a guarantee for regression of the disease, since patients with a normal CA 125 may have progression of the disease. A rise in CA 125 during or after treatment, however, is almost always associated with progression of the disease.

Chondrosarcoma of the jaw and facial bones

BACKGROUND

Osteosarcomas of the jaw frequently have chondroblastic differentiation, causing confusion with chondrosarcomas.

METHOD

Clinicopathologic features and results of treatment were analyzed for a series of 56 patients (27 males and 29 females from 1.5 to 88 years of age) with chondrosarcoma of jaw and facial bones. Twelve patients (21.4%) were younger than 20 years.

RESULTS

The major symptom was nasal obstruction or a painless mass; the median interval from the first symptom until initial treatment was 1 year. Of the 56 chondrosarcomas, 25(44.6%) involved the alveolar portion of the maxilla and maxillary sinus; 23 (41.1%) involved the nasal septum, ethmoid, and sphenoid; 6 (10.7%) involved the mandible; and 2 (3.6%) involved the nasal tip. Of the 19 patients with radiographic studies, 15 (78.9%) had an expanding soft tissue mass with varied matrix calcification and destruction of bone and 2 had a purely lytic lesion. The lesion was difficult to assess in the two others. Most tumors had a lobulated growth pattern of hyaline cartilage. Hypercellularity, nuclear pleomorphism, and binucleation were common features. Forty-three tumors were grade 1, 13 were grade 2, and none were grade 3. Modalities of treatment were known for 51 of the 56 patients. Forty-six patients (90.2%) had surgical treatment, 2 (3.9%) had combination radiation therapy and chemotherapy, 1 (2%) had radiation therapy alone, and 2 (3.9%) had biopsy only. Follow-up adequate for analysis was obtained for 42 patients. Of these, 14 (33.3%) had local recurrence; uncontrolled recurrence developed in 9 (21.4%) patients. No distant metastases were documented. Overall actuarial survival at 5, 10, and 15 years was 80.7%, 65.3%, and 56%, respectively. Survival was analyzed for location, size, and histologic grade of tumor. No statistically significant differences were found.

CONCLUSIONS

Chondrosarcomas of the jaw and facial bones are extremely rare, locally aggressive tumors.

Advanced giant cell granuloma: a twenty-year study

Giant cell granuloma is a benign lesion that generally involves the mandible and maxilla. It may be locally aggressive and result in extensive tissue destruction in advanced cases. A retrospective analysis of giant cell granuloma during the interval 1970 to 1990 revealed 18 cases of advanced disease, as defined by bone destruction and a greatest dimension of 2.0 cm or more. Epidemiologic factors, physical findings, imaging studies, pathologic specimens, treatment modalities, and outcome were reviewed for each case. Eight lesions were treated by local excision and curettage, and 10 were treated by partial mandibulectomy. Five mandibular defects were reconstructed with iliac bone grafts and one with a free flap. Only one patient with maxillary giant cell granuloma who underwent curettage had regrowth of what is suspected to have been residual disease. Individualized treatment, tailoring the extent of resection to the extent of disease, provided excellent results.

[Consensus on the treatment and control of border-line tumors of the ovary in Denmark]

In order to obtain an impression of the consensus in Denmark of the treatment and control of border-line tumours of the ovary (BTO), a questionnaire was sent to all 43 departments of gynaecology/obstetrics and of surgery with gynaecology/obstetrics. Thirty-seven (86%) departments replied. The results of the investigation are presented. It is concluded that about 75% (87% in stage Ia and 65% in stage Ib) perform restrictive surgery on younger patients in the early stages. Indication for chemotherapy is found only in patients with more advanced stages. Very few find an indication for radiotherapy. Treatment and control of BTO in Denmark are in agreement with current international principles.

Obstructive sleep apnea syndrome in patients with class II malocclusion

This study was designed to analyze the effect of class II malocclusion as a factor in the development of obstructive sleep apnea syndrome. Although mandibular retrusion has been reported coincidentally with obstructive sleep apnea syndrome many times, no causal relationship has been established. No previous study has analyzed the occurrence of obstructive sleep apnea syndrome in patients with class II malocclusion without sleep complaints. In this study, we selected 12 patients with class II malocclusion who required surgical mandibular-lengthening or repositioning procedures. These patients were surveyed for sleep habits or sleep complaints and then studied with overnight polysomnography for sleeping or breathing abnormalities. None of these patients had obstructive sleep apnea syndrome. From this sample population, an incidence of obstructive sleep apnea syndrome of no more than 26.5% in the surgical population of patients with class II malocclusion can be extrapolated.

Preoperative donation of autologous blood: technique, experience, and community applications

Preoperative donation of autologous blood (PDAB) is the technique of choice for the transfusion of autologous blood for the maxillofacial surgeon. The use of PDAB is increasing, but lack of preoperative planning and lack of available utilization protocols are obstacles to its more widespread use. A technique for PDAB, a review of our experience, and guidelines for community applications are presented.

Mucocutaneous pigmented spots and oral myxomas: the oral manifestations of the complex of myxomas, spotty pigmentation, and endocrine overactivity

The complex of myxomas, spotty pigmentation, and endocrine overactivity is a recently recognized syndrome, transmitted as an autosomal dominant trait. The most serious component of the disorder is cardiac myxoma, which has caused the death of one fourth of the affected patients and serious disability in an equal number. It is, therefore, important to recognize patients at risk from the syndrome and, in particular, to test them for cardiac myxoma. Fortunately, in many patients the myxoma complex has a clearly visible marker: mucocutaneous pigmentation. Among 58 patients with the syndrome, spotty facial pigmentation was present in 36 (62%), and 29 (50%) of these also had pigmented spots on their lips. This type and distribution of pigmentation should be a clue to the possible presence of the complex of myxomas, spotty pigmentation, and endocrine overactivity, and patients thus affected should be referred for further investigation. Oral cavity myxoma(s) occurred in four patients with the syndrome.

Nitrous oxide neurotoxicity studies in man and rat

To assess the effects of chronic exposure to low levels of nitrous oxide on neural function of man, the authors evaluated the neurologic condition, motor and sensory nerve conduction, and computerized tests of sensation of approximately half of the dentists in Rochester, Minnesota. Results of scored tests of neural function were not significantly different for dentists who used nitrous oxide extensively in their practices and dentists who did not. To assess the effects of chronic exposure to high levels of nitrous oxide on neural function and structure of experimental animals, groups of rats were exposed to 70 per cent N2O in 30 per cent oxygen for four hours, five days a week, for six months. Rats exposed to N2O and control rats showed no difference in well-being, in caudal nerve conduction, in axonal content and transport of acetylcholinesterase and dopamine-beta-hydroxylase, or in number and size distribution and pathologic abnormality of teased myelinated fibers. Although these results indicate a lack of peripheral nerve neurotoxicity of N2O in the rat, one cannot assume a similar lack of neurotoxicity in man with heavy exposures.