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Biomedical subjects

C A Dennis

Publications and source records attributed to C A Dennis.

At least 19 recordsLinked to original sources
PubMed2001

NMR trial models: experiences with the colicin immunity protein Im7 and the p85alpha C-terminal SH2-peptide complex.

Two cases of successful molecular replacement using NMR trial models are presented. One is the crystal structure of the Escherichia coli colicin immunity protein Im7; the other is a heretofore unreported crystal structure of a specific PDGF receptor-derived peptide complex of the carboxy-terminal SH2 domain from the p85alpha subunit of human phosphatidylinositol 3-OH kinase. In both cases, molecular replacement was non-trivial. Success was achieved using trial models that consisted of an ensemble of NMR structures from which the more flexible portions had been excised. Use of maximum-likelihood refinement proved critical to be able to refine the poor starting models. The challenges typical of the use of NMR trial models in molecular replacement are discussed.

Bacterial Proteins↗
PubMed1998

A structural comparison of the colicin immunity proteins Im7 and Im9 gives new insights into the molecular determinants of immunity-protein specificity.

We report the first detailed comparison of two immunity proteins which, in conjunction with recent protein engineering data, begins to explain how these structurally similar proteins are able to bind and inhibit the endonuclease domain of colicin E9 (E9 DNase) with affinities that differ by 12 orders of magnitude. In the present work, we have determined the X-ray structure of the Escherichia coli colicin E7 immunity protein Im7 to 2.0 A resolution by molecular replacement, using as a trial model the recently determined NMR solution structure of Im9. Whereas the two proteins adopt similar four-helix structures, subtle structural differences, in particular involving a conserved tyrosine residue critical for E9 DNase binding, and the identity of key residues in the specificity helix, lie at the heart of their markedly different ability to bind the E9 DNase. Two other crystal structures were reported recently for Im7; in one, Im7 was a monomer and was very similar to the structure reported here, whereas in the other it was a dimer to which functional significance was assigned. Since this previous work suggested that Im7 could exist either as a monomer or a dimer, we used analytical ultracentrifugation to investigate this question further. Under a variety of solution conditions, we found that Im7 only ever exists in solution as a monomer, even up to protein concentrations of 15 mg/ml, casting doubt on the functional significance of the crystallographically observed dimer. This work provides a structural framework with which we can understand immunity-protein specificity, and in addition we believe it to be the first successfully refined crystal structure solved by molecular replacement using an NMR trial model with less than 100% sequence identity.

Amino Acid Sequence↗
PubMed1997

Protein-protein interaction specificity of Im9 for the endonuclease toxin colicin E9 defined by homologue-scanning mutagenesis.

The colicin DNase-specific immunity proteins interact with the endonuclease domain of the bacterial toxin colicin E9 with dissociation constants that span the millimolar to femtomolar affinity range. Among the non-cognate interactions Im2 shows the strongest binding toward the E9 DNase domain with a Kd of 10(-8) M, 6 orders of magnitude weaker than that of the cognate immunity protein Im9. Based on a NMR structure of Im9 that shows it to be a 4-helix protein, we have conducted a mutagenic scan in which elements of Im9 secondary structure were substituted into Im2 to precisely delineate regions that define specificity. Eleven chimeras were constructed, and their biological cross-reactivity toward colicins E2 and E9 was evaluated. From this set of mutants seven proteins were purified, and the Kd for their interaction with the E9 DNase domain was measured by a combination of stopped-flow fluorescence and subunit exchange kinetics. Our results show that immunity specificity is dominated by residues on helix II, accounting for 5 orders of magnitude binding specificity relative to Im2, and that packing interactions of helix II with its neighbor helix I and the loop connecting helix III with helix IV play minor roles. The conformational stability of these chimeric proteins was also determined. Proteins displaying an Im9 phenotype were all more stable than the parent Im2 protein, and surprisingly some chimeras were significantly more stable than either Im2 or Im9.

Amino Acid Sequence↗
PubMed1995

Stress testing with closed-loop arbutamine as an alternative to exercise. The International Arbutamine Study Group.

OBJECTIVES: This study compared exercise and pharmacologic stress testing using arbutamine delivered by a closed-loop device for the detection of coronary artery disease. BACKGROUND: Arbutamine, an agent designed to simulate exercise, has been developed in conjunction with a closed-loop delivery device that modulates the rate of administration on the basis of physiologic feedback. METHODS: Two hundred ten patients (180 men, 30 women) with symptoms and angiographic evidence of coronary artery disease were studied. Ischemia was categorized in three ways: 1) the presence of angina; 2) the occurrence of > or = 0.1-mV horizontal or downsloping ST segment depression or elevation at 60 ms after the J point; or 3) the presence of either condition 1 or 2. RESULTS: In the 210 patients, the mean increase in heart rate and systolic blood pressure evoked by arbutamine and exercise was 51 and 53 beats/min (p = NS) and 36 and 44 mm Hg (p < 0.0001), respectively. Arbutamine detected ischemia more often than exercise with each of the three ischemic end points. Sensitivity for detecting ischemia by either angina or ST segment change was 84% (95% confidence interval ¿ change was 84% (95% confidence interval [CI] 79% to 89%) for arbutamine and 75% (95% CI 69% to 81%) for exercise testing (p = 0.014). For angina alone, sensitivity was 73% (95% CI 67% to 79%) for arbutamine and 64% (95% CI 57% to 71%) for exercise (p = 0.026). For ST segment change alone, sensitivity was 47% (95% CI 40% to 54%) for arbutamine and 44% (95% CI 37% to 51%) for exercise (p = 0.426). Cardiac events occurred in five patients (1.8%) within 24 h of the arbutamine test. CONCLUSIONS: In detecting documented coronary artery disease, the sensitivity of arbutamine testing was equal to that of exercise for the electrocardiographic end point of ST segment change alone. Arbutamine testing was significantly superior to exercise testing for either ST change or angina or for angina alone.

Aged↗
PubMed1994

A case-management system for coronary risk factor modification after acute myocardial infarction.

OBJECTIVE: To evaluate the efficacy of a physician-directed, nurse-managed, home-based case-management system for coronary risk factor modification. DESIGN: Randomized clinical trial in which patients received a special intervention (n = 293) or usual medical care (n = 292) during the first year after acute myocardial infarction. SETTING: 5 Kaiser Permanente Medical Centers in the San Francisco Bay area. PATIENTS: 585 men and women aged 70 years or younger who were hospitalized for acute myocardial infarction. INTERVENTION: In the hospital, specially trained nurses initiated interventions for smoking cessation, exercise training, and diet-drug therapy for hyperlipidemia. Intervention after discharge was implemented primarily by telephone and mail contact with patients in their homes. All medically eligible patients received exercise training; all smokers received the smoking cessation intervention; and all patients received dietary counseling and, if needed, lipid-lowering drug therapy. OUTCOME: Smoking prevalence and plasma low-density lipoprotein cholesterol (LDL) concentrations were measured 2 months after infarction, and functional capacity was measured 6 months after infarction. RESULTS: In the special intervention and usual care groups, the cotinine-confirmed smoking cessation rates were 70% and 53% (P = 0.03), plasma LDL cholesterol levels were 2.77 +/- 0.69 mmol/L and 3.41 +/- 0.90 mmol/L (107 +/- 30 mg/dL and 132 +/- 30 mg/dL) (P = 0.001), and functional capacities were 9.3 +/- 2.4 METS and 8.4 +/- 2.5 METS (P = 0.001), respectively. CONCLUSION: In a large health maintenance organization, a case-management system was considerably more effective than usual medical care for modification of coronary risk factors after myocardial infarction.

Adult↗
PubMed1994

Intracerebral hemorrhage complicating urokinase infusion into an occluded aortocoronary bypass graft.

Selective infusion of urokinase into occluded coronary bypass vein grafts is effective in restoring patency. We report the occurrence of intracerebral hemorrhage complicating an intra-graft urokinase infusion protocol. The patient had known cerebral vascular structural pathology without recent clinical complications. Caution with the use of thrombolysis in this setting is suggested.

Cerebral Hemorrhage↗
PubMed1982

Occupational work evaluation of patients with cardiac disease: a guide for physicians.

The capacity of cardiac patients to work in their occupations reflects a complex interaction of medical and nonmedical factors. Medical considerations include prognosis and the ability of patients to tolerate the physical, environmental and psychological aspects of their occupation. Nonmedical factors include the patient's satisfaction with the job, economic motivation to work and perceived risk of continued work. Patients' perceptions of their capacity to work and the risks of such work are especially important determinants of occupational work status after myocardial infarction and coronary operations. Symptom-limited treadmill exercise testing carried out three to four weeks after the acute event not only clarifies prognosis and quantitates functional capacity but helps patients to realistically assess their capacity for work. Approximately half of postinfarction patients are found by such testing to have a very low first-year mortality of less than 2 percent. Functional capacity is well maintained in these patients: they do not require formal reconditioning in order to resume their occupational work soon (three to five weeks) after infarction. Exercise testing performed soon after myocardial infarction and coronary artery operation affords practical guidelines for clearing a person to return to work and obviates much of the medically unwarranted disability that follows these events.

Angina Pectoris↗
PubMed1976

Low density and high density lipoprotein turnover following portacaval shunt in swine.

Turnover of 125I-low density lipoprotein (LDL) and of 131I-high density lipoprotein (HDL) was determined before and after end-to-side portacaval shunt in eight swine. LDL (d 1.019-1.063) and HDL (d.1.09-1.21) were isolated by ultracentrifugation and iodinated by the iodine monochloride technique. Immediately postoperatively there was no consistent change in the fractional catabolic rate (FCR) of LDL compared to preoperative control values, while in all animals FCR of HDL was significantly increased (by as much as 300%). After recovery from surgery, neither LDL nor HDL catabolic rates were significantly elevated above control values in four swine. However, plasma levels of LDL and HDL protein, and of LDL and HDL cholesterol were significantly reduced 10-12 weeks after the portacaval shunt. The reduced levels of LDL and HDL associated with normal fractional clearance rates imply a reduction in synthesis of LDL and HDL following portal diversion.

Animals↗
PubMed1975

Mercury levels in whole blood of Saskatchewan residents.

The study was undertaken to establish whole blood mercury levels in the Saskatchewan population and to identify characteristics of individuals with higher blood levels. The mean blood mercury level was 6.7 ng/ml, the median level 5 ng/ml and the range 1 to 42 ng/ml. Native persons living in northern Saskatchewan who had recently eaten local fresh-water fish had the higher levels. A greater consumption of fish and higher blood mercury levels were recorded during the fresh-water fishing season.

Adolescent↗
PubMed1975

The relationship between mercury levels in maternal and cord blood.

The object of the study was to discover the relationship between mercury levels in maternal and cord blood. Paired whole blood samples, maternal and cord blood were analysed for total mercury content; 45 paired samples from non-fish-eating women in southern Saskatchewan demonstrated no significant differences in mercury levels between maternal and cord blood; 43 paired samples from fish-eating women in northern Saskatchewan demonstrated a significant difference, cord blood levels being higher. The significant is discussed.

Animals↗