Hierarchy of simulation models in predicting structure and energetics of the Src SH2 domain binding to tyrosyl phosphopeptides.

Structure and energetics of the Src Src Homology 2 (SH2) domain binding with the recognition phosphopeptide pYEEI and its mutants are studied by a hierarchical computational approach. The proposed structure prediction strategy includes equilibrium sampling of the peptide conformational space by simulated tempering dynamics with the simplified, knowledge-based energy function, followed by structural clustering of the resulting conformations and binding free energy evaluation of a single representative from each cluster, a cluster center. This protocol is robust in rapid screening of low-energy conformations and recovers the crystal structure of the pYEEI peptide. Thermodynamics of the peptide-SH2 domain binding is analyzed by computing the average energy contributions over conformations from the clusters, structurally similar to the predicted peptide bound structure. Using this approach, the binding thermodynamics for a panel of studied peptides is predicted in a better agreement with the experiment than previously suggested models. However, the overall correlation between computed and experimental binding affinity remains rather modest. The results of this study show that small differences in binding free energies between the Ala and Gly mutants of the pYEEI peptide are considerably more difficult to predict than the structure of the bound peptides, indicating that accurate computational prediction of binding affinities still remains a major methodological and technical challenge.     

Tissue specific expression of mouse transferrin during development and aging

Transferrin (TF) is a major plasma protein that binds ferric iron and transports it to all target tissues of the body. This study is the first step to identify the tissue specific expression of the transferrin gene in mice during development, into maturity and throughout the aging process. The transferrin gene expresses mainly in mouse liver, the cerebral hemispheres and cerebellum. In mouse, transferrin is expressed in peritoneal macrophages and in mouse macrophage cell line MO59. At 19 days of gestation, transferrin mRNA is detected in the fetal lung, heart, stomach and kidney. TF mRNA levels increase in liver throughout gestation with maximum expression occurring at 19 days. Transferrin mRNA was detected in placentas of pregnant mice, with levels progressively increasing throughout the term of pregnancy. The levels of liver TF mRNA in mouse vary in a cyclic manner during the development increasing with the aging processes. Because of the dynamic nature of tissue requirements for transferrin during homeostasis the TF gene serves as a promising system for analyzing tissue-specific regulation in vivo during development and aging. Results from this study designate periods in the life-span of the mouse where regulatory mechanisms interacting with the TF gene appear to dynamically alter its expression.     

Intrinsic failure of Hancock mitral bioprostheses: 10- to 15-year experience

Hancock porcine bioprostheses have been implanted in the mitral position at the National Institutes of Health since July, 1970. Eight models (330, 330A, 330B, 330C, 332, 340, 341, and 342) were used during a 54-month period ending December, 1974, and 100 consecutive surviving patients were evaluated for subsequent bioprosthetic valve failure and prosthesis-related complications by annual clinic examinations and serial hemodynamic studies. Actuarial patient survival was 76 +/- 4%, 51 +/- 5%, and 30 +/- 6% after 5, 10, and 15 years, respectively. Intrinsic valve failure, defined as structural degeneration of bioprosthetic tissue or stent geometry alteration or both, in the absence of prior infection, occurred in 23 patients. The linear occurrence rate of bioprosthetic valve failure was 0.2%, 5%, and 15% per patient-year, and it affected 1 patient, 14 patients, and 8 patients at sequential 5-year milestones. The actuarial freedom from valve failure was 99 +/- 1%, 75 +/- 6%, 58 +/- 8%, and 40 +/- 12% after 5, 10, 12, and 14 years, respectively. The valve durability of early Hancock bioprostheses (models 330 through 341; N = 39) was not appreciably different from that of the current model 342 valves (N = 61). However, an increased incidence of intrinsic valve failure was observed for the first polypropylene-stented valve type (model 330) compared with the currently available model 342 valve (8/16, 50%, versus 12/61, 20%; p = 0.034). The yearly occurrence rate of prosthesis-related complications remained constant, but the rate of intrinsic valve failure increased in a progressive, nonlinear fashion. The high intrinsic failure rate of the Hancock porcine bioprosthesis after 10 to 12 years has moderated our initial enthusiasm for this valve in the mitral position, and has resulted in more frequent implantations of mechanical valve substitutes at this institution.     

Oscillatory behavior in inferior olive neurons: mechanism, modulation, cell aggregates

Inferior olive neurons, in brain slices maintained in vitro, display spontaneous, continuous oscillations of their membrane potential which are consonant with olivary rhythmic activity seen in vivo. This oscillatory behavior was studied with intracellular electrophysiological techniques. The 3-10 Hz rhythmicity of these cells from guinea pigs is tetrodotoxin resistant and dependent on a somatic calcium conductance. The oscillatory behavior can exhibit intrinsic frequency modulation and can be altered by synaptic processes. Synaptic alteration of the oscillatory behavior by afferent sources and extensive electrotonic coupling between cells in local aggregates (shown by Lucifer yellow dye-coupling) provide the substrate for a potent central pattern generator with a well established efferent pathway for control of motor functions.     

Sexual, reproductive and contraceptive risk factors for carcinoma-in-situ of the uterine cervix in Sydney

Sexual, reproductive and contraceptive risk factors were investigated in a matched community-based case-control study of carcinoma-in-situ of the uterine cervix in Sydney. The risk was related strongly to the number of sexual partners: women who had had seven or more sexual partners in a lifetime had a six-fold increased risk compared with those with one or no partner. Early age at first sexual intercourse was also a risk factor, but this effect was reduced substantially after adjustment for the number of partners, with only a two-fold excess risk persisting for those with first intercourse before the age of 16 years as compared with those whose first sexual intercourse was at the age of 25 years or later. The long-term use of oral contraceptive agents was associated with an elevated risk (relative risk, 2.3 for more than six years of use); this effect was maintained for both oestrogen and progestogen doses. The risk increased with the number of induced abortions that had been undergone (relative risk, 2.2 for two or more abortions), but this effect was not statistically significant. A protective effect was found for women who had had a tubal ligation, for those who practised the rhythm method of birth control, and for women who breastfed. It is possible that these reduced risks may relate to unmeasured variables of life-style.     

Dauerwirkung einer Einmaligen Hormondosis

Ohne Zusammenfassung