Thermodynamics of core hydrophobicity and packing in the hyperthermophile proteins Sac7d and Sso7d.

The influence of core hydrophobicity and packing on the structure and stability of the hyperthermophile proteins Sac7d and Sso7d have been studied by calorimetry, circular dichroism, and NMR. Valine 30 is positioned in Sac7d to allow a cavity-filling Val --> Ile substitution which occurs naturally in the homologous more thermostable Sso7d. The cavity-filling mutation in Sac7d has been characterized and compared to the reciprocal Ile --> Val mutation in Sso7d. A detailed analysis of the stability of the proteins was obtained by globally fitting the variation of DSC parameters and circular dichroism intensities as a function of temperature (0-100 degrees C), salt (0-0.3 M), and pH (0-8). A global analysis over such a range of conditions permitted an unusually precise measure of the thermodynamic parameters, as well as the separation of the thermodynamics of the intrinsic unfolding reaction from the linked effects of protonation and chloride binding associated with acid-induced folding. The results indicate differences in the energetics of unfolding Sac7d and Sso7d that would not be apparent from an analysis of DSC data alone using conventional methods. The sign and magnitude of the changes in DeltaG, DeltaH, TDeltaS, and DeltaC(P) of unfolding resulting from core Ile/Val substitutions in the two proteins were consistent with differences in hydrophobicity of Val and Ile and negligible changes in packing (van der Waals) interactions. The benefit of increased hydrophobicity of the core increased with temperature, with maximal effect around 116 degrees C. Increased hydrophobicity of the core achieved not only an increase in the free energy of unfolding, but also a lateral shift of the temperature of maximal stability to higher temperature.

The use of color-flow duplex scan for the detection of endoleaks.

OBJECTIVE: Computed tomographic (CT) scan represents the criterion standard for surveillance of endoleaks after endoluminal repair of abdominal aortic aneurysms (erAAAs). Given need for surveillance, risks, and expense of CT scan, the accuracy of color-flow duplex (CFD) scan after erAAA was determined. METHODS: During a 43-month period, patients enrolled in phase II and III of the AneuRx Multicenter Clinical Trial at our institution underwent CFD scan 1 month after erAAA. Patients with CFD scan results that were positive for endoleak underwent CT scanning at 3 months after erAAA, and those with CFD scan results that were negative for endoleak underwent CT scanning at 6 months after erAAA. RESULTS: Seven of 79 patients (9%) who underwent CFD and CT scanning had the diagnosis of endoleak. All endoleaks that were diagnosed with CT scan were detected with CFD scan. One patient had positive results for endoleak with CFD scan at 1 month and then negative results with CT scan at 3 months. Although this may represent resolution of endoleak, this case was counted as a false-positive result. When compared with CT scan, CFD scan had a sensitivity of 100%, specificity of 99%, positive predictive value of 88%, negative predictive value of 100%, and accuracy of 99%. CONCLUSION: CFD scan is an accurate test for the detection of endoleak after erAAA. In addition, most endoleaks diagnosed with CFD scan at 1 month continued to be present at 6 months. This important finding increases the emphasis on the use of this noninvasive test and may initiate earlier intervention of endoleak.