Effective critical micellar concentration of a zwitterionic detergent: A fluorimetric study on n-dodecyl phosphocholine

We have investigated the effect of ionic strength on the aggregation behavior of n-dodecyl phosphocholine. On the basis of the classical Corrin-Harkins relation, the critical micellar concentration of this detergent decreases with a biphasic trend on lithium chloride addition. It is nearly constant below 150 mM salt, with a mean value of 0.91 mM, whereas it undergoes a dramatic 80-fold decrease in 7 M LiCl. Such a drop in the critical micellar concentration could be explained by the effect of salting out and the implication of phosphocholine head groups on the organization of surrounding water. Knowledge of the effective critical micellar concentration of n-dodecyl phosphocholine could be useful in the purification of membrane proteins in non-denaturing conditions

Enthalpy-entropy balance and convergence temperatures in protein unfolding.

We find that isoenthalpic and isoentropic temperatures characterizing the unfolding of small globular proteins are linked by a simple relationship, which takes into account the occurrence of common values of specific unfolding enthalpy and entropy changes. The difference between these temperatures implies that the hydration effect favors protein folding over a quite large range of temperatures

The concentration of homocysteine-derived disulfides in human coronary artery

*Background* 
Based on previous findings, we have estimated that, in injured coronary artery tissue, the low molecular weight disulfides homocystine and cysteine-homocysteine, otherwise identified as oxidized homocysteine equivalents (OHcyE), may achieve a total concentration that is higher than the aqueous solubility of homocystine at room temperature. In order to verify whether or not OHcyE could reach their saturation limit in the vascular tissue, we have measured the solubility of homocystine in physiological-like condition.

*Materials and methods* 
The solubility of homocystine has been measured in aqueous sodium chloride solutions at 37 °C by differential pulse polarography based on the reduction of homocystine to homocysteine.

*Results* 
We have estimated that the concentration achieved by OHcyE in injured coronary artery tissue is at least near-saturating, because the solubility of homocystine in physiological-like condition, above which deposition of homocystine and/or cysteine-homocysteine as solid phase occurs, almost exactly matches its value. Near-saturation levels of OHcyE within the vascular tissue means that significant leakage of intracellular fluid can promote OHcyE crystallization in tissue fluids, which may serve to initiate inflammation. 

*Conclusions* 
We speculate that deposition of OHcyE crystals could damage blood vessels and act as a primer of homocysteine-triggered inflammation, thus being along the causal pathway that leads to vascular dysfunction

NMR Structure and CD Titration with Metal Cations of Human Prion α2-Helix-Related Peptides

The 173–195 segment corresponding to the helix 2 of the C-globular prion protein domain could be one of several “spots” of intrinsic conformational flexibility. In fact, it possesses chameleon conformational behaviour and gathers several disease-associated point mutations. We have performed spectroscopic studies on the wild-type fragment 173–195 and on its D178N mutant dissolved in trifluoroethanol to mimic the in vivo system, both in the presence and in the absence of metal cations. NMR data showed that the structure of the D178N mutant is characterized by two short helices separated by a kink, whereas the wild-type peptide is fully helical. Both peptides retained these structural organizations, as monitored by CD, in the presence of metal cations. NMR spectra were however not in favour of the formation of definite ion-peptide complexes. This agrees with previous evidence that other regions of the prion protein are likely the natural target of metal cation binding

Prospective validation of the CLIP score: a new prognostic system for patient with cirrhosis and hepatocellular carcinoma

Prognosis of patients with cirrhosis and hepatocellular carcinoma (HCC) depends on both residual liver function and tumor extension. The CLIP score includes Child-Pugh stage, tumor morphology and extension, serum alfa-fetoprotein (AFP) levels, and portal vein thrombosis. We externally validated the CLIP score and compared its discriminatory ability and predictive power with that of the Okuda staging system in 196 patients with cirrhosis and HCC prospectively enrolled in a randomized trial. No significant associations were found between the CLIP score and the age, sex, and pattern of viral infection. There was a strong correlation between the CLIP score and the Okuda stage, As of June 1999, 150 patients (76.5%) had died. Median survival time was 11 months, overall, and it was 36, 22, 9, 7, and 3 months for CLIP categories 0, 1, 2, 3, and 4 to 6, respectively. In multivariate analysis, the CLIP score had additional explanatory power above that of the Okuda stage. This was true for both patients treated with locoregional therapy or not. A quantitative estimation of 2-year survival predictive power showed that the CLIP score explained 37% of survival variability, compared with 21% explained by Okuda stage. In conclusion, the CLIP score, compared with the Okuda staging system, gives more accurate prognostic information, is statistically more efficient, and has a greater survival predictive power. It could be useful in treatment planning by improving baseline prognostic evaluation of patients with RCC, and could be used in prospective therapeutic trials as a stratification variable, reducing the variability of results owing to patient selection

Homocysteine disulphides and vascular disease

The total plasma concentration of homocysteine is a marker of this amino acid's atherogenic potential. However, the homocysteine pool exists almost entirely as oxidized homocysteine equivalents (OHcyE), composed of homocystine and cysteine-homocysteine disulphides (20-30%), and protein-bound disulphide (70-80%). We have noticed that the total concentration of OHcyE in injured coronary artery tissue is higher than the aqueous solubility of homocystine (similar to 1.4-1.5 x 10(-3) mol kg(-1) versus similar to 0.6 mol kg(-1)). Based on the measurement of the solubility of homocystine in a plasma-mimetic condition (0.17 mol kg(-1) NaCl at 37 degrees C), we have estimated that OHcyE may really reach their saturation limit in the vascular tissue (0.93-1.02 x 10(-3) mol kg(-1)), above which their deposition as solid phase may occur. This means that significant leakage of intracellular fluid can promote OHcyE crystallization in tissue fluids, which may serve to initiate inflammation. We speculate that deposition of OHcyE crystals could damage blood vessels and act as a primer of homocysteine-triggered inflammation, thus being along the causal pathway that leads to vascular dysfunction

A thermodynamic approach to the conformational preferences of the 180–195 segment derived from the human prion protein α2-helix

cited By 7International audienceOn consideration that intrinsic structural weakness could affect the segment spanning the α2-helical residues 173-195 of the PrP, we have investigated the conformational stabilities of some synthetic Ala-scanned analogs of the peptide derived from the 180-195 C-terminal sequence, using a novel approach whose theoretical basis originates from protein thermodynamics. Even though a quantitative comparison among peptides could not be assessed to rank them according to the effect caused by single amino acid substitution, as a general trend, all peptides invariably showed an appreciable preference for an α-type organization, consistently with the fact that the wild-type sequence is organized as an α-helix in the native protein. Moreover, the substitution of whatever single amino acid in the wild-type sequence reduced the gap between the α- and the β-propensity, invariably enhancing the latter, but in any case this gap was larger than that evaluated for the full-length α2-helix-derived peptide. It appears that the low β-conformation propensity of the 180-195 region depends on the simultaneous presence of all of the Ala-scanned residues, indirectly confirming that the N-terminal 173-179 segment could play a major role in determining the chameleon conformational behavior of the entire 173-195 region in the PrP. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd