GRAFTER: a computational aid for the design of novel proteins

The GRAFTER suite of programs provides geometric search and evaluation functions that simplify and automate the process of identifying the best scaffolds for a particular structural motif. Three application of the GRAFTER suite are presented. Potential grafts between lambda repressor and 434 repressor were identified that should change the DNA binding specificity of these repressors. These results are compared with site-directed mutagenesis experiments that have been shown to alter repressor-DNA binding specificity. Next, 26 loops from antibody structures were grouped into families of similar structure. Grafts of antibody loops onto a pre-existing scaffold are an essential component of antibody humanization. Finally, interleukin (IL)-4 was searched as a scaffold that might accept the graft of a five residue epitope from human growth hormone (hGH). The existence of a crystal structure of the hGH-hGH receptor complex, extensive mutagenesis studies of the hGH residues that contribute to the energetics of ligand-receptor interactions and the gross structural homology between hGH and IL-4 make this an appealing computational target. The approach presented here could aid the development of novel enzymes and binding proteins.     

Right ventricular radiofrequency ablation of ventricular tachycardia after myocardial infarction

Radiofrequency transcatheter ablation of ventricular tachycardia in the setting of a prior myocardial infarction is typically performed with application of energy to the left ventricular endocardium. In this article, two cases are described in which successful radiofrequency transcatheter ablation of ventricular tachycardia occurred with energy delivery to the right ventricular septum after failed ablation attempts from the left ventricle. Both patients had tachycardias with a left bundle branch block morphology and markedly presystolic activity recorded from the right ventricular septum. Right ventricular septal activation mapping during ventricular tachycardia should be performed in patients with left bundle branch block tachycardia morphology and coronary artery disease to maximize efficacy of the catheter ablation procedure.     

Body composition and age in African-American and Caucasian women: relationship to plasma leptin levels

Leptin is a recently isolated peptide hormone released from adipocytes that has been postulated to play a role in appetite regulation and energy metabolism. Aging affects both food intake and body composition. Body composition is also affected by ethnicity. We have evaluated the relationships between serum leptin levels, age, body composition (by dual-energy x-ray absorptiometry), and hormonal parameters in a cross-sectional study of 94 women, 53 African-American (AAF) and 41 Caucasian (CF). Our hypotheses were as follows: (1) changes in body composition would be related to age in a sinusoidal pattern, (2) changes in serum leptin would parallel changes in body fat, (3) serum leptin levels would be influenced by body fat distribution, and (4) serum leptin would be related to serum concentrations of sex hormones. Serum leptin paralleled changes in body fat and body mass index (BMI) with age. In the entire group, serum leptin correlated closely with measures of body fat, including BMI and total fat mass, and there was no difference in leptin levels between the two ethnic groups. In simple regression analysis, serum leptin was related to both serum estradiol and testosterone. The relationship between serum leptin and trunk fat was linear in both groups, but significantly different in AAF and CF (P = .014). Serum leptin was associated with the trunk to lower-extremity fat ratio in CF (r = .67, P = .001) but not in AAF. Body fat was increased with advancing age until about 65 years and then declined. Measures of lean body mass declined linearly with age in the entire group, as well as both subgroups. In the entire group, total lean body mass and lean body mass corrected for BMI (lean body mass/BMI) were inversely related to age. In subjects aged less than 60 years AAF were stronger (P < .05) and had both a larger BMI and fat mass (P < .05) than CF. However, the patterns of age-related changes in fat body mass, lean body mass, and BMI were similar in both groups. In the entire group, multiple regression analysis indicated that the age, free thyroxine index (FTI), and leptin concentration were predictors of the body composition and distribution of trunk to lower-body fat. These observations indicate that there is a sinusoidal relationship between body fat and age, with a decline in body fat in extreme old age in both AAF and CF, and that serum leptin concentrations are more closely related to body fat and BMI than to age or ethnicity.     

Postshock sensing performance in transvenous defibrillation lead systems: analysis of detection and redetection of ventricular fibrillation

INTRODUCTION: The sensing performance of transvenous lead systems may be adversely affected by the delivery of high-energy shocks. This may be due to the proximity of the sensing and energy-delivery electrodes on transvenous leads. METHODS AND RESULTS: The time required for detection of ventricular fibrillation and redetection after a failed first shock was compared in 93 patients with five different lead system-pulse generator combinations: Cadence--Endotak 60 series, Ventak P--Endotak 60 series, Jewel--Transvene, Cadence--TVL, and Cadence--Transvene. A total of 418 successful and 204 failed first shocks were delivered during induced ventricular fibrillation. Redetection times (RED) were consistently shorter than detection times (DET) in the Jewel-Transvene (RED minus DET: -1.9 +/- 0.8 sec, P < 0.0001), the Cadence-TVL (-1.6 +/- 1.0 sec, P < 0.0001), and the Cadence-Transvene combinations (-2.0 +/- 0.9 sec, P < 0.0004). Redetection times were not significantly different than detection times in the Cadence-Endotak combination (0.9 +/- 3.1 sec; P = 0.09). Redetection times were significantly longer than detection times in the Ventak-Endotak combination (1.2 +/- 2.3 sec; P = 0.034). Prolonged individual redetection episodes (> 8.2 sec) were observed in the Cadence-Endotak (7 [10%] of 73 episodes) and the Ventak-Endotak (4 [10%] of 39 episodes), but not in the Jewel-Transvene, the Cadence-TVL, and the Cadence-Transvene combinations. CONCLUSIONS: Redetection of ventricular fibrillation may be delayed in some transvenous lead-pulse generator combinations. Successful redetection of ventricular fibrillation following a failed first shock should be demonstrated prior to hospital discharge of patients with implantable defibrillators.     

A cdc15-like adaptor protein (CD2BP1) interacts with the CD2 cytoplasmic domain and regulates CD2-triggered adhesion

A human CD2 cytoplasmic tail-binding protein, termed CD2BP1, was identified by an interaction trap cloning method. Expression of CD2BP1 is restricted to hematopoietic tissue, being prominent in T and natural killer (NK) cells, with long (CD2BP1L) and short (CD2BP1S) variants arising by alternative RNA splicing. Both CD2BP1 molecules are homologous to Schizosaccharomyces pombe cdc15, and include a helical domain, variable length intervening PEST sequence and C-terminal SH3 domain. Although the CD2BP1 SH3 domain binds directly to the CD2 sequence, KGPPLPRPRV (amino acids 300-309), its association is augmented markedly by the CD2BP1 N-terminal segment. Upon ligand-induced clustering of surface CD2 molecules, CD2BP1 redistributes from a cytosolic to a surface membrane compartment, co-localizing with CD2. In turn, CD2-stimulated adhesion is downregulated by CD2BP1, apparently through coupling of the protein tyrosine phosphatase (PTP)-PEST to CD2. These findings offer the first molecular view into the control processes for T cell adhesion.     

Risk of acute myelogenous leukaemia and myelodysplasia following cancer treatment

Now that a substantial group of cancer patients has such a favourable prognosis, it has become increasingly important to evaluate the long-term complications of treatment. Of all late effects of treatment, secondary leukaemia is one of the most serious. Increased risk of AML has been observed both after RT and after CT; however, several types of CT have much stronger leukaemogenic properties than RT. Limited field radiation in the therapeutic dose range is associated with very little or no increased risk of leukaemia, which has been attributed to cell killing at the higher radiation doses. With respect to CT, two different syndromes of treatment-related AML have been recognized. Risk of alkylating agent-related AML is highest in the 5-10 year follow-up period and seems to decrease afterwards. This type of leukaemia is often preceded by MDS, and is characterized by deletions of chromosomes 5 and 7. Leukaemias related to treatment with the topoisomerase II inhibitors are characterized by a short induction period, presentation as myelomonocytic or monocytic leukaemia (rather than MDS) and balanced chromosomal translocations involving bands 11q23 and 21q22. This review addresses the risk of secondary AML and MDS following treatment of HD, NHL, testicular cancer, ovarian cancer, breast cancer and paediatric malignancies. In patients with HD, the risk of AML is higher with an increasing number of mechlorethamine-procarbazine-containing cycles, a greater number of CT episodes, and after splenectomy. The majority of data shows that RT does not add to the leukaemia risk from CT, but this issue is still surrounded by some controversy. ABV(D)-treated patients have a very low risk of AML. Generally, patients with NHL, testicular cancer and breast cancer experience much lower risk of AML than patients with HD. NHL and breast cancer treatment regimens with cumulative cyclophosphamide doses of 20 g or less do not confer an appreciable increase of AML. Recently, strongly increased AML risk has been observed following autologous bone marrow transplantation and other dose intensification strategies. Risk factors for this excess remain to be defined. PVB treatment for testicular cancer is not followed by increased leukaemia risk, but modern etoposide-containing regimens do confer excess risk, of which the magnitude at conventional drug doses is not yet well known. High risk of leukaemia has been reported in children treated with epipodophyllotoxins. The leukaemogenic hazards of cancer treatment should be weighed against their therapeutic benefits.     

Measurement of the ultrasonic attenuation of fat at high frequency

RATIONALE AND OBJECTIVES: High-frequency ultrasound devices are often limited by a decreased depth of acoustic imaging caused by the increased attenuation of tissue at high frequencies. We investigated the role of adipose tissue in this phenomenon. METHODS: A substitution technique was used to calculate the ultrasonic attenuation (decibels per centimeter) of fresh samples of sheep rumen, omental fat, and back fat and swine back fat and various concentrations of bovine milk fat at 22 degrees C and 37 degrees C for frequencies of 15 and 20 MHz. RESULTS: The attenuation was significantly higher for sheep adipose tissue than for the intestinal wall, in descending order, omental fat, back fat, and rumen wall (P < 0.01). A correlation was found between bovine milk fat concentrations and attenuation at both frequencies (R2 > 0.9). The attenuation of adipose tissues decreased significantly with an increase in temperature (P < 0.01), whereas the attenuation of sheep rumen showed no significant change (P > 0.1). CONCLUSIONS: The ultrasonic attenuation of fat may contribute to limitations on the use of high-frequency ultrasound in clinical situations in which adipose tissue is present.