Optimization of accelerated testing through design of experiment for ageing of lead-free electronic interconnection material

Understanding the ageing of materials for electronic application is a complex challenge, in particular for composite material as electrically conductive adhesive consisting of a nonconductive polymer binder and conductive filler particles. This research involves a large amount of parameters related to both operating conditions and material structure, which act together. Accelerated testing, with the aim to consume rapidly lifetime without inducing incorrect failure mechanisms, is difficult to optimize and its modelling to describe the ageing process is a challenge. To reach this aim could be interesting for the characterization of the material but above all for the general validity of the proposed methodology.

Extremely preterm births: end-of-life decisions in European countries

OBJECTIVE

To explore the influence of end-of-life decisions (EoL-D) on survival and mortality data in the light of differences reported among European countries.

DESIGN

We collected the published data of several epidemiological studies: Epicure, Epipage, Epibel and the Norwegian study performed in the UK, France, Belgium and Norway, respectively. The data concerning the Epibel and Norwegian studies are considered for a preliminary analysis, while the data relating to the Epicure and Epipage studies are compared based on the total published data. The statistical analysis was performed through the class of generalised linear models, and more specifically, through log-linear models. The data considered were the number of babies who died in neonatal intensive care units after active withdrawal classified according to the country and gestational age. RESULTS The probability of death after active withdrawal was significantly higher at 22 and 24 weeks' gestational age compared with week 25, when considering both countries (OR, 2.35 and 1.29, respectively). For the week 23(0)-->(6), the probability of death after active withdrawal was not significant; however, it is relevant when considering the OR (1.31). When considering the country, there was a higher probability of death after active withdrawal in France than in the UK, or alternatively, with the assumed baseline French parameter, in the UK, there was a lower probability of death after active withdrawal, with a significant OR=0.69. CONCLUSIONS The attitude towards EoL-D could in part explain the differences in survival data of extremely preterm infants and should be taken in mind when comparing international survival rates.

Inflammatory mediators and eosinophilia in atopic and non-atopic patients with nasal polyposis

Nasal polyps are characterized by eosinophilic infiltration and presence of inflammatory mediators, such as total IgE, eosinophil cationic protein (ECP) and cytokines. The role of atopy in nasal polyp pathogenesis is still unclear. Therefore, we evaluated serum IgE levels, nasal mucus concentrations of ECP and cytokines and the number of infiltrating eosinophils in nasal tissue of polyps from atopic and non-atopic patients. Samples were obtained from a randomized population of 31 patients with nasal polyposis having endonasal sinus surgery and of 13 control subjects undergone corrective surgery of the nasal septum. On the basis of medical history of allergy, positive skin-prick tests and total IgE levels, patients with polyposis were divided in atopic (n = 13) and non-atopic (n = 18) patients. We determined levels of IgE in blood, ECP and cytokines (IL-4, IL-6, IL-8, IFN-gamma and IL-2) in nasal mucus, and number of infiltrating eosinophils in nasal tissue. The concentrations of total IgE, ECP, IL-4 and IL-8 and eosinophilia were significantly higher in all patients with nasal polyps compared with controls. Inside, all patients with nasal polyposis showed lower levels of IL-6, IFN-gamma and IL-2 compared with controls. The atopic patients showed significant differences when compared with non-atopic patients for the higher concentrations of total IgE (698.80+/-322.24 vs. 279.63+/-234.11; P < 0.0001) and IL-8 (1437.2 pg/ml+/-1250.7 vs. 605.5 pg/ml+/-481.1; P < 0.015). These findings suggest that inflammation still remains the major factor in the etiology of nasal polyposis and show different levels of inflammatory mediators into atopic and non-atopic patients.

Structure of chicken plasma retinol-binding protein

The crystal structure of the specific carrier of retinol (retinol-binding protein, RBP) purified from chicken plasma has been determined (space group P2(1)2(1)2(1), with a=46.06(5) A, b=53.56(6) A, c=73.41(8) A, and one protein molecule in the asymmetric unit). Despite being obtained from a species phylogenetically distant from mammals, chicken holoRBP has an overall structure that closely resembles the previously determined structures of mammalian holoRBPs. The lack in chicken RBP of eight carboxy-terminal amino acid residues characteristic of mammalian RBPs does not significantly affect the protein structure. A distinctive feature of the avian protein is a better definition of the loop 63-67, close to the opening of the beta-barrel cavity accommodating the retinol molecule, which is rather disordered in the structures of mammalian RBPs.

Social stress, myocardial damage and arrhythmias in rats with cardiac hypertrophy

In rat models of cardiac hypertrophy (moderate aortic coarctation: ACm, n=18; severe aortic coarctation: ACs, n=27; aging: OLD, n=25; spontaneous chronic hypertension: SHR, n=18) and properly matched control animals (C(ACm), n=17; C(ACs), n=19; C(OLD), n=24; C(SHR), n=22), we investigated the relative contribution of intense autonomic activity and cardiac structural damage to ventricular arrhythmogenesis. We used an "in vivo" to tissue level approach, by correlating in the same animal: (i) social stress-induced ventricular arrhythmias, telemetrically recorded, and (ii) left ventricular weights (LVW) and amount and geometrical properties of myocardial fibrosis (MF). Arterial blood pressure was significantly higher in ACm (+11%), ACs (+28%) and SHR (+34%) than in controls. LVW were approximately 20% greater in ACm, ACs and OLD and 50% greater in SHR. MF was about twice as great and characterized by more frequent occurrence of microscopic scarring in ACm and ACs, and eight times greater and associated with both a higher number and a larger size of fibrotic foci in OLD and SHR compared to controls. Social stress increased ventricular arrhythmia vulnerability in all models of cardiac hypertrophy, as well as in controls. The arrhythmogenic action of stress was facilitated in ACs, OLD and SHR. A correlation between structural cardiac remodeling and ventricular arrhythmias was found only in SHR and OLD, which exhibited the greatest increase in LVW and/or MF. Social stress proved to be a valuable tool for analyzing the combined effects of autonomic stimulation and altered myocardial substrate on the genesis of potentially life-threatening arrhythmias in social animals.

Identification, retinoid binding, and x-ray analysis of a human retinol-binding protein

Two cellular retinol-binding proteins (CRBP I and II) with distinct tissue distributions and retinoid-binding properties have been recognized thus far in mammals. Here, we report the identification of a human retinol-binding protein resembling type I (55.6% identity) and type II (49.6% identity) CRBPs, but with a unique H residue in the retinoid-binding site and a distinctively different tissue distribution. Additionally, this binding protein (CRBP III) exhibits a remarkable sequence identity (62.2%) with the recently identified iota-crystallin/CRBP of the diurnal gecko Lygodactylus picturatus [Werten, P. J. L., Röll, B., van Alten, D. M. F. & de Jong, W. W. (2000) Proc. Natl. Acad. Sci. USA 97, 3282-3287 (First Published March 21, 2000; 10.1073/pnas.050500597)]. CRBP III and all-trans-retinol form a complex (K(d) approximately 60 nM), the absorption spectrum of which is characterized by the peculiar fine structure typical of the spectra of holo-CRBP I and II. As revealed by a 2.3-A x-ray molecular model of apo-CRBP III, the amino acid residues that line the retinol-binding site in CRBP I and II are positioned nearly identically in the structure of CRBP III. At variance with the human CRBP I and II mRNAs, which are most abundant in ovary and intestine, respectively, the CRBP III mRNA is expressed at the highest levels in kidney and liver thus suggesting a prominent role for human CRBP III as an intracellular mediator of retinol metabolism in these tissues.

Specific interaction of lipoate at the active site of rhodanese

Dihydrolipoate is an acceptor of the rhodanese-bound sulfane sulfur atom, as shown by analysis of the elementary steps of the reaction catalyzed by rhodanese. The crystal structure of sulfur-substituted rhodanese complexed with the non-reactive oxidized form of lipoate has revealed that the compound is bound at the enzyme active site, with the dithiolane ring buried in the interior of the cavity and the carboxylic end pointing towards the solvent. One of the sulfur atoms of the ligand in the unproductive complex is relatively close to the sulfane sulfur bound to Cys-247, the sulfur that is transferred during the catalytic reaction. This mode of binding of lipoate is likely to mimic that of dihydrolipoate. The results presented here support the possible role of dihydrolipoate as sulfur-acceptor substrate of rhodanese in an enzymatic reaction that might serve to provide iron-sulfur proteins with inorganic sulfide.

Structure at 1.44 A resolution of an N-terminally truncated form of the rat serum complement C3d fragment

Complement component C3 plays a key role in the complement-mediated immune defence, and occupies a central position within the complement cascade system. One of its degradation products, C3dg, was purified from rat serum and crystallised in two different crystal forms as N-terminally truncated fragment. Despite the truncation and the lack of a significant portion of the N-terminus as compared to C3d, the structure of the fragment is highly similar to that of recombinant human C3d (Nagar et al., Science 280 (1998) 1277-1281). Structural details of the reactive site have been obtained, suggesting a possible mode of thioester bond formation between Cys-1010 and Gln-1013 and thioester bond cleavage in the transacylation reaction involving His-1126. The truncation at the N-terminus of C3d leads to the exposure of a surface of the molecule that favours dimerisation, so that in both crystal forms, the fragment is present as a dimer, with monomers related by a two-fold axis.

NH2-terminal sequence truncation decreases the stability of bovine rhodanese, minimally perturbs its crystal structure, and enhances interaction with GroEL under native conditions

The NH2-terminal sequence of rhodanese influences many of its properties, ranging from mitochondrial import to folding. Rhodanese truncated by >9 residues is degraded in Escherichia coli. Mutant enzymes with lesser truncations are recoverable and active, but they show altered active site reactivities (Trevino, R. J., Tsalkova, T., Dramer, G., Hardesty, B., Chirgwin, J. M., and Horowitz, P. M. (1998) J. Biol. Chem. 273, 27841-27847), suggesting that the NH2-terminal sequence stabilizes the overall structure. We tested aspects of the conformations of these shortened species. Intrinsic and probe fluorescence showed that truncation decreased stability and increased hydrophobic exposure, while near UV CD suggested altered tertiary structure. Under native conditions, truncated rhodanese bound to GroEL and was released and reactivated by adding ATP and GroES, suggesting equilibrium between native and non-native conformers. Furthermore, GroEL assisted folding of denatured mutants to the same extent as wild type, although at a reduced rate. X-ray crystallography showed that Delta1-7 crystallized isomorphously with wild type in polyethyleneglycol, and the structure was highly conserved. Thus, the missing NH2-terminal residues that contribute to global stability of the native structure in solution do not significantly alter contacts at the atomic level of the crystallized protein. The two-domain structure of rhodanese was not significantly altered by drastically different crystallization conditions or crystal packing suggesting rigidity of the native rhodanese domains and the stabilization of the interdomain interactions by the crystal environment. The results support a model in which loss of interactions near the rhodanese NH2 terminus does not distort the folded native structure but does facilitate the transition in solution to a molten globule state, which among other things, can interact with molecular chaperones.

Crystallization and preliminary X-ray data for the human transthyretin-retinol-binding protein (RBP) complex bound to an anti-RBP Fab

A macromolecular complex of human transthyretin, human retinol-binding protein and an anti-retinol-binding-protein Fab was crystallized by vapour diffusion in sitting drops. Diffraction from these crystals at cryogenic temperatures was consistent with the space group C222, with cell parameters a = 159.34, b = 222.40 and c = 121.27 A. Crystals diffracted to a resolution limit of 3.36 A using synchrotron radiation. Based on a 2:2:1 stoichiometry for the Fab-retinol-binding-protein-transthyretin complex and the presence of one such complex per asymmetric unit, a reasonable Vm coefficient of 2.74 A3 Da-1 could be estimated.

Structure of pig plasma retinol-binding protein at 1.65 A resolution

The crystal structure of pig plasma retinol-binding protein (RBP) has been determined at 1.65 A resolution. The space group is P212121, with a = 45.81 (4), b = 53.14 (5), c = 72.97 (8) A and one protein molecule in the asymmetric unit. The structure has been solved using the molecular replacement method and refined with restrained least squares to an R factor of 0.1844 and an Rfree of 0.237 for 18 874 and 1001 independent reflections, respectively. The relatively high resolution structure of pig holoRBP has revealed some new structural details. Moreover, it has provided a description of the binding site for Cd2+, a metal ion which is required for protein crystallization. The hepta-coordination of the RBP-bound cadmium ion involves different residues of two symmetry-related RBP molecules, consistent with the participation of the cation in intermolecular interactions that in turn promote protein crystallization.

Structure of sulfur-substituted rhodanese at 1.36 A resolution

1.36 A resolution X-ray diffraction data have been recorded at 100 K for bovine liver sulfur-substituted rhodanese, using synchrotron radiation. The crystal structure has been refined anisotropically to a final R factor of 0.159 (Rfree = 0.229) for 53034 unique reflections. The model contains 2327 protein atoms and 407 solvent molecules, with a good geometry. The high resolution allows full details for helices, beta-sheets, tight turns and of all inter- and intramolecular interactions stabilizing the enzyme molecule to be given. The situation at the active site is described, particularly in regard to the network of hydrogen bonds made by Sgamma and Sdelta of the sulfur-substituted catalytic Cys247 and surrounding groups and solvent molecules. The replacement of the precipitant ammonium sulfate with cryoprotectants in the crystal-suspending medium led to the removal of the sulfate ion from the enzyme active site. Only limited changes of the enzyme structure have been found as a result of the drastic change in the crystal medium.

Structure of the trigonal crystal form of bovine annexin IV

The structure of a trigonal crystal form of N-terminally truncated [des-(1-9)] bovine annexin IV, an annexin variant that exhibits the distinctive property of binding both phospholipids and carbohydrates in a Ca2+-dependent manner, has been determined at 3 A (0.3 nm) resolution -space group: R3; cell parameters: a=b=118.560 (8) A and c=82.233 (6) A-. The overall structure of annexin IV, crystallized in the absence of Ca2+ ions, is highly homologous to that of the other known members of the annexin family. The trimeric assembly in the trigonal crystals of annexin IV is quite similar to that found previously in non-isomorphous crystals of human, chicken and rat annexin V and to the subunit arrangement in half of the hexamer of hydra annexin XII. Moreover, it resembles that found in two-dimensional crystals of human annexin V bound to phospholipid monolayers. The propensity of several annexins to generate similar trimeric arrays supports the hypothesis that trimeric complexes of such annexins, including annexin IV, may represent the functional units that interact with membranes.

Active site structural features for chemically modified forms of rhodanese

In the course of the reaction catalyzed by rhodanese, the enzyme cycles between two catalytic intermediates, the sulfur-free and the sulfur-substituted (persulfide-containing) forms. The crystal structure of sulfur-free rhodanese, which was prepared in solution and then crystallized, is highly similar to that of sulfur-substituted enzyme. The inactivation of sulfur-free rhodanese with a small molar excess of hydrogen peroxide relies essentially on a modification limited to the active site, consisting of the oxidation of the essential sulfhydryl to sulfenyl group (-S-OH). Upon reaction of the sulfur-free enzyme with monoiodoacetate in the crystal, the Cys-247 side chain with the bound carboxymethyl group is forced into a conformation that allows favorable interactions of the carboxylate with the four peptide NH groups that participate in hydrogen bonding interactions with the transferable sulfur atom of the persulfide group in the sulfur-substituted rhodanese. It is concluded that active site-specific chemical modifications of sulfur-free rhodanese do not lead to significant changes of the protein structure, consistent with a high degree of similarity of the structures of the sulfur-free and sulfur-substituted forms of the enzyme both in solution and in the crystal.

Retinoid binding to retinol-binding protein and the interference with the interaction with transthyretin

The retinol carrier retinol-binding protein (RBP) forms a complex with the thyroid hormone binding protein transthyretin in the plasma of a number of vertebrate species. The interactions of retinoid-RBP complexes, as well as of unliganded RBP, with transthyretin have been investigated by means of fluorescence anisotropy studies. The presence of two independent and equivalent RBP binding sites per transthyretin molecule has been established for proteins purified from species distant in evolution. Although the natural ligand retinol participates in the interaction between retinol-RBP and transthyretin, its binding to RBP is not a prerequisite for protein-protein interaction. The dissociation constants of human transthyretin binding liganded and unliganded forms of human RBP were determined to be: all-trans retinol-RBP, Kd approximately 0.2 microM; apoRBP, Kd approximately 1.2 microM; all-trans retinoic acid-RBP, Kd approximately 0.8 microM; all-trans retinyl methyl ether-RBP, Kd approximately 6 microM. The complex of RBP with the synthetic retinoid fenretinide, which bears the bulky hydroxyphenyl end group, exhibits negligible affinity for transthyretin. The replacement of RBP-bound retinol with synthetic retinoids affects RBP-transthyretin recognition to an extent that appears to be well correlated with the nature and steric hindrance of the groups substituting the retinol hydroxyl group, consistent with their location at the interface between the contact areas of RBP and transthyretin.

Crystal structure of the transthyretin--retinoic-acid complex

Retinoids are quite insoluble and chemically unstable compounds in the aqueous medium, such that natural retinoids need to be bound to specific retinoid-binding proteins to be protected, solubilized and transported in body fluids. All-trans retinoic acid exhibits a relatively high affinity for thyroxine-binding transthyretin in vitro and this protein is a good candidate for the transport of retinoic acid administered as pharmacological or antitumor agent. To define structural features essential for the recognition by transthyretin of a ligand which is structurally unrelated to thyroxine, we have cocrystallized human transthyretin with retinoic acid and determined its structure at 0.18-nm resolution. The retinoid fits into the two chemically identical thyroxine-binding sites, which are located in the central channel that runs through the tetrameric transthyretin. The cyclohexene ring of the bound retinoid is innermost, occupying the same position of the phenolic ring of the bound 3,3'-diiodo-L-thyronine, whereas the carboxylate group, like the same group of the thyroid hormone, participates in an ionic interaction with the Lys15 side chain at the entrance of the channel. Despite the fact that transthyretin was cocrystallized with all-trans-retinoic acid, the isoprene chain of the bound retinoid has been found in a non-extended conformation. This feature, that allows the carboxylate to orient in a manner suitable for ion-pair association with the Lys15 side chain, is attributable to the conversion of all-trans-retinoic acid into cis-isomers or folded conformers. It is concluded that the presence, in an essentially hydrophobic molecular core of the appropriate size, of a negatively charged group at the correct position is a crucial requirement for ligand-transthyretin recognition. Whereas the binding of the ligand has no remarkable consequences for the protein structure, all-trans-retinoic acid undergoes structural changes such as to interact favorably with residues present in the thyroxine-binding sites, resembling roughly the natural ligand.

[An increase in bile acids in the serum of patients with chronic kidney failure]

Measurement of serum bile acids was performed in 86 uremic patients without any liver or bile tract diseases. Thirty-six patients (23 males and 13 females, aged 21-60 years) were on conservative dietary treatment, whereas 50 uremics (31 males and 19 females, aged 23-82 years) were on maintenance hemodialysis. The assays were made by means of enzymatic procedure and confirmed by RIA method too. Elevated serum concentrations of bile acids (> 6 mumol/L) were found in 24 out of the 86 uremics (27.9%), and the prevalence was similar in patients on conservative (10/36, 27.7%) and on dialysis treatment (14/50, 28%). Then, abnormally elevated concentrations of circulating bile acids are present in a quite high percentage of uremics both on hemodialysis and on conservative dietary therapy. The existence of a subclinical liver disease or an abnormal entero-hepatic cycle of bile acids might explain these findings.

Interactions with retinol and retinoids of bovine cellular retinol-binding protein

The interactions with retinol and retinol analogs of bovine cellular retinol-binding protein (CRBP) have been investigated, by means of fluorescence titrations, to obtain more information on the structural features of retinoid that may be required for their interaction with the binding protein. An approximately stoichiometric binding of retinol to bovine CRBP (K'd approximately 2 nM) has been found in direct binding assays. Although retinal exhibited relatively high binding affinity to bovine CRBP (K'd approximately 30 nM), a large excess of the retinoid could not compete with retinol for the carrier protein. On the assumption that retinol and retinal interact with the same binding site, this result indicates that the above-mentioned apparent dissociation constant for retinol.CRBP may be an overestimate and that its value may be as low as 0.1 nM. The finding of an exceedingly tight binding of retinol to CRBP provides further support for the possible role of CRBP-bound retinol, rather than its uncomplexed labile form, as substrate of enzymes involved in the metabolism of the vitamin. The results of these and previous studies indicate that CRBP is particularly sensitive to modifications of the retinol hydroxyl end group. Axerophthene, a retinol analog bearing a hydrogen atom in place of the hydroxyl end group, and beta-ionone exhibit rather low binding affinities for CRBP (K'd approximately 0.2 microM and approximately 4 microM, respectively), suggesting that the hydroxyl group and isoprene tail moieties contribute substantially to the retinol-binding affinity and specificity. These findings are consistent with the indications emerging from the three-dimensional structure determination of retinol.CRBP [Cowan, S. W., Newcomer, M. E. & Jones, T. A. (1993) J. Mol. Biol. 230, 1225-1246]. Additionally, the bulky end groups of fenretinide and N-ethyl retinamide replacing the retinol hydroxyl group have been found to prevent retinoid binding to CRBP. The primary structure of bovine CRBP has been determined and is highly similar to the structures of both human and rat CRBP (97% and 95% identical, respectively).

Crystallographic studies on complexes between retinoids and plasma retinol-binding protein

The three-dimensional structures of complexes between bovine plasma retinol-binding protein (RBP) and three retinol analogs with different end groups (fenretinide, all-trans retinoic acid, and axerophthene) have been determined to 1.8-1.9-A resolution. Their models are very similar to that of the bovine retinol.RBP complex: the root mean square deviations between equivalent alpha-carbons in the two proteins range from 0.17 to 0.24 A. The retinoid molecules fit in the beta-barrel cavity assuming the same conformation of the vitamin, and the substitutions have no consequences on the overall protein structure. While confirming that an intact hydroxyl end group is not an absolute requirement for a correct retinoid binding to RBP, this study has shown the occurrence of conformational changes, although limited, in the rather flexible loop region at the entrance of the beta-barrel upon fenretinide and retinoic acid binding. These changes are suitable for accommodating the end groups of the above retinoids. Instead, no such changes have been revealed in RBP complexed with axerophthene, a retinol analog bearing a hydrogen atom in place of the hydroxyl end group. The protein conformational changes in the above loop region, the steric hindrance of bulky end groups of bound retinoids, and the lack of the retinol hydroxyl group appear to be responsible for the possible reduced affinity of retinoids for RBP relative to retinol and, at the same time, for the abolished or reduced affinity of retinoid.RBP complexes for transthyretin relative to retinol-RBP.

The Ile-84-->Ser amino acid substitution in transthyretin interferes with the interaction with plasma retinol-binding protein

In plasma the thyroid hormone-binding protein transthyretin (TTR) forms a tight complex with the specific retinol carrier retinol-binding protein (RBP). The Ile-84-->Ser mutation and several other point mutations in TTR are associated with familial amyloidotic polyneuropathy, which is characterized by extracellular depositions of amyloid fibrils mainly consisting of mutated TTRs. The interactions with human RBP of recombinant human normal and Ser-84 TTRs were investigated by monitoring the fluorescence anisotropy of RBP-bound retinol. A nearly negligible affinity of the recombinant Ser-84 TTR for RBP was found. This result indicates the participation of a region on the outer surface of TTR that comprises Ile-84 in the recognition of RBP. In preliminary studies the Ser-84 TTR was the only one among several amyloidogenic variant TTRs to display negligible interaction with RBP. Therefore, in general a substantially altered binding of TTR to RBP is not associated with familial amyloidotic polyneuropathy. Instead, the altered binding of Ser-84 TTR to RBP appears to be responsible for an abnormal plasma transport of RBP. The recombinant normal TTR exhibits binding properties, in its interaction with human RBP, approximately similar to those of TTR purified from human plasma. Two independent and equivalent RBP binding sites on recombinant normal TTR are characterized by a dissociation constant of about 0.4 microM.

The interaction of N-ethyl retinamide with plasma retinol-binding protein (RBP) and the crystal structure of the retinoid-RBP complex at 1.9-A resolution

The three-dimensional structure of bovine plasma retinol-binding protein (RBP) complexed with N-ethyl retinamide has been determined at 1.9-A resolution. The crystals of the complex (space group P2(1)2(1)2(1), a = 46.27, b = 49.11, c = 76.41 A) are isomorphous with those of bovine holo and apoRBP. The final crystallographic R factor is 0.172 for 11,261 observed reflections. The model of the retinoid-RBP complex is nearly identical to that of bovine retinol-RBP complex; the root mean square deviations between the alpha-carbons in the two proteins is 0.15 A. The N-ethyl retinamide molecule fits in the beta-barrel in the same position previously occupied by the vitamin. The ethyl group of the retinoid replaces the retinol hydroxyl group and a water molecule hydrogen bonded to it. This substitution has no consequence on the overall conformation of the protein. The modification of the functional end group of retinol does not lead to an apparent loss of affinity of the retinol analog for apoRBP, as established by means of fluorometric titrations with N-ethyl retinamide. However, the binding of the retinoid to RBP abolishes or greatly reduces the affinity of RBP for transthyretin. This behavior further supports the hypothesis that the area of the entrance of the beta-barrel, which includes the ethyl group of the retinoid bound to RBP, is involved in the interaction with transthyretin. Moreover, it indicates a high degree of complementarity of interacting surfaces between RBP and transthyretin. In fact, the replacement of the retinol hydroxyl group and quite small structural changes in the above region of the RBP molecule drastically affect the protein-protein recognition.

Retinoids: in vitro interaction with retinol-binding protein and influence on plasma retinol

Studies have been conducted to investigate the structure-function relationships of retinoids in their in vitro interaction with plasma retinol-binding protein (RBP) and in their influence on plasma retinol concentration. Two classes of retinoids, one bearing modifications in the area of the retinol hydroxyl end group (fenretinide, N-(ethyl) retinamide, all-trans, and 13-cis retinoic acid) and the other one also bearing modifications in the area of the cyclohexene ring (etretinate, acitretin, and arotinoid Ro 13-7410), were investigated. Whereas substantial modifications of the retinol hydroxyl group do not prevent the binding to RBP, an intact trimethylcyclohexenyl group seems to be crucial for binding. Both classes of retinoids, administered orally at equimolar doses, reduce plasma retinol concentration in rats but with different kinetics. A marked lowering of plasma retinol occurs early (within 5 h) after administration of retinoids that interact with RBP in vitro, whereas it occurs at later times (24 h) after retinoids that do not interact with RBP. The concentrations of both classes of retinoids found in plasma do not account for the temporal difference in this effect. The early reduction of plasma retinol might be the consequence of in vivo specific binding of retinoids to RBP, as suggested by the in vitro results. The late reduction observed for retinoids lacking in vitro affinity for RBP is due to other mechanisms or to metabolism to retinoids binding to RBP.

Crystal structure of liganded and unliganded forms of bovine plasma retinol-binding protein

The three-dimensional structures of bovine plasma retinol-binding protein (bRBP) complexed with retinol (space group P2(1)2(1)2(1), a = 46.08, b = 49.12, c = 76.10 A) and of the unliganded protein prepared in vitro by extracting retinol with ethyl ether (space group P2(1)2(1)2(1), a = 46.55, b = 48.97, c = 76.87 A) have been solved at 1.9 and 1.7 A resolution, respectively. The final crystallographic R factors are 0.190 for holobRBP and 0.196 for the unliganded bRBP. The model for the bovine holoprotein is quite similar to that of the human protein, with which it exhibits 92% sequence similarity. The root mean square deviation between the alpha-carbons in the two proteins is 0.31 A. The retinol binding site is almost completely preserved. The loops that surround the opening of the beta-barrel are also particularly conserved, in contrast with the presence of several substitutions in parts of the RBP molecule opposite the opening of the calyx that binds retinol. Despite the fact that unliganded bovine RBP was prepared and crystallized using procedures completely different from those used to obtain the unliganded human RBP, the conformational differences between unliganded and liganded forms of bRBP are almost identical to those found previously between the same forms of human RBP. They mainly involve a few residues in the region extending from amino acid residues 32 to 37. Therefore, similar differences are very likely to exist between holoRBP and the physiologically occurring apoprotein. A not yet identified electron density, different in shape and orientation from retinol, also occupies the central cavity of the beta-barrel in the unliganded bRBP, as found for unliganded human RBP. The functional consequences of the conformational change induced by the removal of retinol on the interaction between RBP and transthyretin, coupled with the conservation of the entrance loops of the beta-barrel in mammalian RBPs, are consistent with their participation in molecular interactions.

Crystal structure of the trigonal form of human plasma retinol-binding protein at 2.5 A resolution

The three-dimensional structures of the liganded and unliganded forms of human plasma retinol binding protein (RBP) in the trigonal crystal form have been solved at 2.5 A resolution. The final model of RBP complexed with retinol (holoRBP, space group R3, a = b = 104.0 A, c = 74.4 A) has a crystallographic R factor of 0.176 for 9652 reflections. The unliganded form, obtained through a purification procedure which included steps based on hydrophobic interaction chromatography, crystallized isomorphously with holoRBP and its structure has been refined to an R factor of 0.190 for 9614 reflections. The structure of the trigonal holo protein is quite similar to that of the orthorhombic form: the root-mean-square deviation of all the equivalent alpha-carbons in the two chains is 0.53 A. The structural comparison between the liganded and unliganded forms of RBP in the crystal did not reveal gross conformational changes. The most significant difference between the two forms of the protein is a conformational change involving residues from 34 to 37. In this region, the movements of side-chains of Leu35 and Phe36 are most noticeable. In particular, in the unliganded form the side-chain ring of the latter residue is in the place previously occupied by the alcoholic moiety of retinol. Our data are consistent with a model in which a region comprising these residues and at least part of the opening of the beta-barrel is involved in the recognition between RBP and transthyretin. In the case of the unliganded form, the central cavity, that is occupied by the vitamin in the two human crystalline holoRBPs, is filled by electron density that, at the present resolution, we interpret as solvent.

The primary structure of piscine (Oncorhynchus mykiss) retinol-binding protein and a comparison with the three-dimensional structure of mammalian retinol-binding protein

1. The primary structures of two variants of rainbow trout (Oncorhynchus mykiss) plasma retinol-binding protein (RBP) were determined and found to be approximately 60% identical with those of both human and Xenopus laevis RBPs. The comparable sequence similarities that we have found agree with the estimate of similar divergence times between bony fishes and mammals and between bony fishes and amphibians. The two piscine RBP variants differ by six amino acid substitutions at positions that are not crucial for the interaction with retinol, on the basis of the human RBP three-dimensional structure [Cowan, S. W., Newcomer, M. E. & Jones, T. A. (1990) Proteins Struct. Func. Genet. 8, 44-61]. 2. Models were developed for the three-dimensional structures of rainbow trout and X. laevis RBPs, based on that of human RBP. The overall three-dimensional structure appears to be very well preserved for RBPs isolated from vertebrate species for which the divergence time is 350-400 million years. At variance with an almost absolute conservation for the residues that participate in the formation of the retinol binding site in mammalian RBPs, several amino acid replacements are found for this part of the RBP molecule when the comparison is extended to piscine and amphibian RBPs. However, the only allowed amino acid replacements are either conservative or more than 0.4 nm distant from retinol. Besides the retinol binding site, a few regions at the protein surface appear to be rather conserved during phylogenetic development of vertebrates and, therefore, might be involved in molecular interactions.

IgE modification of the specific antidermatophagoides during the first year of specific immunotherapy (SIT)

Six subjects (4 female, 2 male), aged from 16 to 25 years, presented with allergic rhinitis to Dermatophagoides mites and received SIT by the sub-cutaneous route with delayed-release alpha fraction Bayropharm at the standard doses. Diagnosis was based on clinical history, skin tests and measurement of specific IgE at 0, 3, 9, and 12 months, by the fluoro-enzymatic technique (FAST). For comparison, in a reference group (n = 20) the IgE varied between 0.32 and 0.11 IU/ml for D1 and 0.31 to 0.09 IU/ml for D2. The eight patients had specific IgE titres of D1 = 0.96, D2 = 0.99. For these authors, the FAST technique used for the measurement of specific IgE, although less sensitive than the RIA technique of RAST, gives a good evaluation of SIT.

Retinol-binding protein is in the molten globule state at low pH

Using far- and near-UV circular dichroism, viscosity, tryptophan fluorescence, NMR spectra, binding of a hydrophobic probe, and microcalorimetry, we have shown that the apo form of human retinol-binding protein (RBP) at neutral pH is in a rigid state with properties similar to those of holo-RBP. On the contrary, at acidic pH apo-RBP is in the molten globule state which has been earlier revealed for a number of proteins under mild denaturing conditions. We have also shown that, at equilibrium, the pH-induced retinol release from holo-RBP parallels denaturation of the apoprotein. These findings are consistent with our hypothesis that the transformation of RBP into the molten globule state is involved in the mechanism whereby retinol is delivered to target cells. In particular, a local acidic pH near the membrane surface of target cells might cause the transition of RBP to the molten globule state as well as the release of retinol.

In vitro interaction of fenretinide with plasma retinol-binding protein and its functional consequences

The synthetic retinoid fenretinide (4-HPR; N-[4-hydroxyphenyl] all-trans-retinamide) interacts with plasma apo-retinol-binding protein (RBP) to form a tight complex (K'd approximately 0.2 microM) which does not exhibit binding affinity to transthyretin (TTR). Therefore, a substantial modification of the retinol hydroxyl group does not appear to affect the interaction with RBP but does drastically interfere with the protein-protein recognition. The remarkable early reduction in plasma retinol level induced by fenretinide administration may be associated with the high binding affinity of this retinoid to RBP and to its interference with the RBP-TTR complex formation.

The piscine plasma retinol-binding protein. Purification, partial amino acid sequence and interaction with mammalian transthyretin of rainbow trout (Oncorhynchus mykiss) retinol-binding protein

1. Retinol-binding protein (RBP) has been isolated from the pooled plasma or rainbow trouts (Oncorhinchus mykiss) by gel filtration, hydrophobic interaction chromatography and ion-exchange chromatography. By this procedure two forms of the protein, both with a molecular mass (approximately 20 kDa) similar to that of mammalian RBP, were purified to homogeneity. Five amino acid substitutions have been found in the partial (about 60%) sequences of the two forms of trout RBP, which are presumably acetylated at their N terminus. The apparent participation of six conserved cysteines in the formation of disulphide bridges, as in human RBP, and the similarity (about 60%) of the amino acid sequence of trout and mammalian RBPs, indicate the existence of a similar overall structure organization in evolutionary distant RBPs. 2. Although the two forms of trout RBP are not physiologically involved in the formation of any protein--protein complex in plasma, they are capable of interacting with mammalian transthyretin, albeit with a binding affinity (K'd = 15-40 microM) considerably lower than that of mammalian RBP. Our data indicate that the two forms of trout RBP also possess the region that in mammalian RBP has the functional role of binding transthyretin. It is suggested that transthyretin (or a homologous protein) was modified, during phylogenetic development of the non mammalian vertebrates, to acquire a binding site for such a region of the RBP molecule.

Chemical modification of rhodanese with sulphite

The essential sulphydryl group of bovine liver rhodanese (thiosulphate: cyanide sulphurtrasferase, E.C. 2.8.1.1.) is modified by sulphite produced during the enzymatic reaction or added to the fully active enzyme. The enzyme treated with labelled reagent incorporates 1 equivalent of SO3(2-) and loses one -SH group with the formation of a S-sulphonate group at the active site. Mercaptoethanol is effective in both restoring enzyme activity and removing bound sulphite from protein. The inactivation process is dependent on the presence of oxygen and is antagonized by chelation of metal ions, that catalyze sulphite autoxidation, or by scavenging free radicals with mannitol or benzoate. Since the presence of superoxide dismutase and/or catalase protects the enzyme only to a small extent, the inactivation process should be attributed to sulphite radicals rather than intermediates of oxygen reduction.

The bovine plasma retinol-binding protein. Amino acid sequence, interaction with transthyretin, crystallization and preliminary X-ray data

1. The primary structure of bovine plasma retinol-binding protein (RBP) has been determined and found to be more than 90% identical to human and rabbit RBPs, and more than 80% identical to rat RBP. Main changes in amino acid sequence are observed in two regions on the surface of the protein molecule (residues 138-148 and 169-183). 2. The interactions of bovine RBP with bovine and human transthyretins were investigated using the technique of fluorescence polarization. Bovine RBP was able to form high affinity complexes (K'd = 0.34 +/- 0.02 microM) with both bovine and human transthyretins, displaying a stoichiometry of approximately 2 molecules RBP/molecule transthyretin in both cases. The sites that participate in protein-protein interactions are thus very similar, and this tends to exclude the involvement of the superficial regions more significantly substituted in mammalian RBPs (residues 138-151 and 167-183) in the protein-protein recognition. 3. Bovine RBP has been crystallized (space group P2(1)2(1)2(1), with a = 4.61 nm, b = 4.91 nm, c = 7.61 nm) and the crystals are suitable for high-resolution X-ray diffraction studies.

Measurement of urinary albumin excretion (UAE) in diabetic patients: immunonephelometry versus radioimmunoassay

We have compared the chemico-clinical characteristics of an immuno-nephelometric technique (INA) with those of a solid-phase radioimmunoassay (RIA) method for the measurement of urinary albumin excretion (UAE) in diabetic patients. The UAE was evaluated in 227 diabetics; all, except 9, were Albustix-negative. The calibration of the nephelometer apparatus every time before the assay did significantly improve the accuracy and precision of the INA method. Similar values were obtained with the two methods (INA = 2.1 + 0.95 RIA, n = 227, r = 0.969) through all the ranges of albumin concentration explored. INA seems as suitable as RIA for the assay of UAE in diabetics. The two methods are comparably accurate and precise. However, RIA appears more sensitive than INA, while immunonephelometric system is easier and faster to perform (up to 200 samples can be assayed in about 1 hour, while 2-4 hours are necessary with RIA), with fewer handling steps. The INA instrumentation is automated and the reagents are more stable and less hazardous than those used in RIA. However, due to the cost of the nephelometer apparatus, the INA technique may be employed by those laboratories which have already this instrumentation or by those which will use it in the next future for the assay of other analytes in addition to albumin.

Dissociation of the bovine serum retinol-binding protein-transthyretin complex and purification of the two interacting proteins

1. Retinol-binding protein is present in bovine serum essentially in the complexed form, bound to transthyretin, as in the case of the other mammalian retinol-binding proteins. 2. Bovine retinol-binding protein-transthyretin complex has the distinctive property of undergoing dissociation in the course of the DEAE-Sephadex chromatography of serum proteins. Therefore, the isolation of uncomplexed retinol-binding protein upon chromatography on this resin cannot represent evidence for lack of binding between it and TTR in bovine plasma, in contrast with previously reported conclusions (Heller J. (1975) J. biol. Chem. 250, (6549-6554). 3. Purified bovine retinol-binding protein and transthyretin can reconstitute a tight complex.

Kinetic evidence for a reversible isomerization of pig muscle glyceraldehyde-3-phosphate dehydrogenase in its crystallization medium

Ammonium sulfate, a typical component of crystallization media of proteins, stabilizes an inactive conformation of pig muscle glyceraldehyde-3-phosphate dehydrogenase. In fact, in the presence of ammonium sulfate the reconstitution of the catalytically active holoenzyme from the apoenzyme and NAD is not instantaneous, as in the case of enzymes from Bacillus stearothermophilus and the Mediterranean lobster Palinurus vulgaris. With pig muscle enzyme, at pH 6.0, the time course of formation of the characteristic Racker band can be monitored by a rapid mixing stopped flow technique. Activation follows a single exponential curve with a rate constant independent of the concentration of both NAD and protein and, therefore, appears to be limited by a slow protein isomerization (k = 7 +/- 2 s-1). Accordingly, when the apoenzyme is simultaneously exposed to NAD and either glyceraldehyde 3-phosphate or 1,3-bisphosphoglycerate, the ensuing reactions (the redox and the acylation steps, respectively) are kinetically limited by the same protein isomerization. At pH 7.0 and 8.0, however, two among the four active sites react with NAD at an unmeasurably high rate, while the other two sites behave as they do at pH 6.0. When the pig muscle apoenzyme is preincubated and allowed to react with either glyceraldehyde 3-phosphate or 1,3-bisphosphoglycerate before the rapid mixing with NAD, both the redox reaction and the NAD-dependent activation of apo-acyl-enzyme toward arsenolysis become unmeasurably fast. Similarly, when the sulfate in the medium is replaced by ions such as phosphate and citrate, the reconstitution of the active holoenzyme is practically instantaneous. Thus, the slow protein isomerization observed in the presence of sulfate and abolished by competing substrates and anions is diagnostic of a structural state of the pig muscle apoenzyme, which is induced by sulfate ions bound within the enzyme active site.

Active site modifications quench intrinsic fluorescence of rhodanese by different mechanisms

Beef liver rhodanese can be modified covalently at the active site (Cys-247) either reversibly or irreversibly by sulfur, selenium, iodoacetate, and hydrogen peroxide. Each derivative shows an intrinsic fluorescence lower than that of the free enzyme. The reaction of rhodanese with iodoacetate or hydrogen peroxide is time-dependent and accompanied by enzyme inactivation, by the loss of one or two sulfhydryl groups, respectively, by quenching and bathochromic shift of fluorescence, and by an absorbance perturbation in the near UV. The latter findings are indicative for a displacement of some tryptophyl side chains from hydrophobic to hydrophilic environment. The fluorescence decays of the various rhodanese derivatives can be fitted by a double-exponential function with two lifetimes: a shorter one of 1-1.7 ns and a longer one of 2.8-4.6 ns. The S-loaded and Se-loaded rhodanese samples have proportionally shorter lifetimes and lower quantum yields. No such proportionality was observed for the iodoacetate-treated and for the hydrogen peroxide treated enzyme. These findings indicate that two different quenching mechanisms are operating in rhodanese derivatives, a long-range energy transfer from tryptophan to persulfide (or sulfoselenide) group and a static quenching accompanying a conformational change of the protein after modification of the active site.

Purification of human plasma retinol-binding protein by hydrophobic interaction chromatography

Human plasma retinol-binding protein has been purified to homogeneity by a simple method that requires an ammonium sulfate fractionation, a hydrophobic interaction chromatography on phenyl-Sepharose, which dissociates the complex between retinol-binding protein and its carrier, transthyretin, and a gel filtration on Sephadex G-50. The yield of pure protein is comparable or higher than that obtained with the more complex procedures previously reported.

Determination of rhodanese activity by tetrazolium reduction

A colorimetric method for the assay of rhodanese activity based on the continuous determination of the sulfite product is described. 5-Ethylphenazinium ethyl sulfate is used as the intermediate electron carrier between sulfite and nitroblue tetrazolium to produce the colored reduced species. The present method is more sensitive than the usual procedure based on the colorimetric determination of thiocyanate. Furthermore, the color developed by nitroblue tetrazolium reduction affords a straightforward means to locate rhodanese activity in polyacrylamide gels.

Crystallization of human plasma apo-retinol-binding protein

Crystals of three forms of human plasma apo-retinol-binding protein have been obtained using the procedure described for the holoprotein. The apoprotein was prepared by a novel method, which uses hydrophobic interaction and immobilized dye chromatography. The three forms were separated by fast protein liquid chromatography. All of the crystals are isomorphous and diffract to 2.5 A resolution. These crystals will be useful for studies of the mechanism of binding of retinol to its carrier using X-ray diffraction techniques.

Interaction of rhodanese with intermediates of oxygen reduction

Cyanide-promoted inactivation of the enzyme rhodanese [thiosulfate sulfurtransferase (EC 2.8.1.1)] in the presence of ketoaldehydes is caused by reduced forms of molecular oxygen generated during autoxidation of the reaction products. The requirement of both catalase and superoxide dismutase to prevent rhodanese inactivation indicates that hydroxyl radical could be the most efficient inactivating agent. Rhodanese, also in the less stable sulfur-free form, shows a different sensitivity towards oxygen activated species. While the enzyme is unaffected by superoxide radical, it is rapidly inactivated by hydrogen peroxide. The extent of inactivation depends on the molar ratio between sulfur-free enzyme and oxidizing agent. Fully inactive enzyme is reactivated by reduction with its substrate thiosulfate.

Micturition monitor as an aid to management of neurogenic bladder

A portable, battery-operated micturition monitor has been developed for use by patients with spinal cord injuries. The monitor, when integrated into the external urinary collection device for a male with a spinal cord injury, provides an accurate measure of the elapsed time in minutes since the patient last voided. This measure greatly reduces the efforts required by the medical staff to obtain a reliable residual urine volume measurement.