Erectile dysfunction post-radical prostatectomy - a challenge for both patient and physician

Post-radical prostatectomy erectile dysfunction (post RP ED) is a major postoperative complication with a great impact on the quality of life of the patients. Until present, no proper algorithm or guideline based on the clinical trials has been established for the management of post RP ED. According to literature, it is better to initiate a penile rehabilitation program as soon as possible after surgery than doing nothing, in order to prevent and limit the postoperative local hypoxygenation and fibrosis. The results of numerous clinical trials regarding the effectiveness of the phosphodiesterase 5 inhibitors therapy on post RP ED have made them the gold standard treatment. Encouraging results have been achieved in studies with vacuum erectile devices, intraurethral suppositories with alprostadil and intracavernosal injections, but due to their side effects, especially in the cases of intracavernosal injections and intraurethral suppositories, their clinical use was limited therefore making them a second line option for the post RP ED treatment. What should not be forgotten is that penile implant prosthesis has proven very effective, numerous studies confirming high rates of satisfaction for both patients and partners.

Thromboangiitis obliterans - case report

Thromboangiitis obliterans (Buerger'€™s disease) represents an inflammatory disease of limbs'€™ small arteries and veins causing vascular thrombosis, and partial or total obstruction. It affects mostly male gender aged 40 years old. The peculiarity of our case is underlined by presenting a 62 years, chronic tobacco user and not compliant female patient known with thromb oangiitisobliterans for almost 15 years. The arteriographic and clinical features with concomitant and sever affected upper and lower limbs are highly suggestive, emphasizing the possibility of Buerger'€™s disease development even in female patients.

Determining factors of diuresis in chronic kidney disease patients initiating hemodialysis

BACKGROUND

Patients with stage 5 chronic kidney disease (CKD) begin chronic hemodialysis with variable diuresis levels correlated to a comparable low glomerular filtration rate. Residual diuresis influences long-term evolution of the hemodialyzed patient, modifying the prognosis even if optimal Kt/ V is achieved.

AIM OF THE STUDY

The present study emphasizes the main determining factors of diuresis in a cohort of stage 5 CKD subjects at the beginning of hemodialysis.

MATERIAL AND METHODS

216 patients with stage 5 CKD starting chronic hemodialysis were included in the study, and were grouped according to their residual diuresis: group A (urine output ≤ 500 mL/ day); group B (urine output between 500-1200 mL/ day); group C (urine output ≥ 1200 mL/ day).

RESULTS

Glomerular etiology, cardiac systolic dysfunction, severe malnutrition, emergency dialysis initiation and lack of permanent vascular access were proved to be associated with significant low diuresis. Age, gender, estimated glomerular filtration rate (GFR) and the presence of systemic hypertension did not influence the amount of daily diuresis.

CONCLUSIONS

In CKD stage 5 patients, residual diuresis presents large variations in conditions of comparable low GFR. Factors influencing residual diuresis may be distinct from those that influence residual GFR.

A rare case of watermelon stomach in woman with continuous ambulatory peritoneal dialysis and systemic lupus erythematosus

We report a case of a 42-year-old woman with systemic lupus erythematosus and chronic kidney disease stage 5 undergoing continuous ambulatory peritoneal dialysis, presenting asthenia, dizziness, abdominal pain and small efforts dyspnea. After a complete physical and clinical examination, including laboratory tests, esophagogastroduodenal endoscopy and gastric lesions biopsy, she was diagnosed with gastric antral vascular ectasia. We are facing a rare case of antral vascular ectasia in a patient associating both chronic kidney disease and autoimmune disease.

Correlation between albuminemia, natremia and survival rates in patients with hepatorenal syndrome

A two years prospective study was developed, based on the monitoring of 84 patients with cirrhosis and elevated serum creatinine; 33 patients met the diagnostic criteria for the hepatorenal syndrome. In these 33 patients, survival rate has been studied in correlation with hepatorenal syndrome types, serum albumin and natremia.

Isotopic labeling of recombinant proteins expressed in the protozoan host Leishmania tarentolae

Isotope labeling of recombinant proteins is a prerequisite for application of nuclear magnetic resonance spectroscopy (NMR) for the characterization of the three-dimensional structures and dynamics of proteins. Overexpression of isotopically labeled proteins in bacterial or yeast host organisms has several drawbacks. In this work, we tested whether the recently described eukaryotic protein expression system based on the protozoa Leishmania tarentolae could be used for production of amino acid specific (15)N-labeled recombinant proteins. Using synthetic growth medium we were able to express in L. tarentolae and purify to homogeneity (15)N-valine labeled Enchanced Green Fluorescent Protein (EGFP) with the final yield of 5.7 mg/liter of suspension culture. NMR study of isolated EGFP illustrated the success of the labeling procedure allowing identification of all 18 valine residues of the protein in the HSQC spectrum. Our results demonstrate the suitability of the L. tarentolae expression system for production of isotopically labeled proteins.

A genetically encodable microtag for chemo-enzymatic derivatization and purification of recombinant proteins

Efficient separation of recombinant polypeptides from proteins of the expression host and their subsequent derivatisation with functional chemical groups is essential for the success of many biological applications. Numerous tag systems have been developed to facilitate the purification procedure but only limited progress has been made in development of generic methods for targeted modification of proteins with functional groups. In this work, we present a novel 6 amino acid long C-terminal protein tag that can be selectively modified with functionalized derivatives of farnesyl isoprenoids by protein farnesyltransferase. The reaction could be performed in complex protein mixtures without detectable unspecific labeling. We demonstrate that this modification can be used to purify the target protein by over 800-fold in a single purification step using phase partitioning. Moreover, we show that the fluorescent group could be used to monitor the interaction of the derivatized proteins with other polypeptides.

Structure of the Rab7:REP-1 Complex

Members of the RabGDI/REP family serve as multifunctional regulators of the Rab family of GTP binding proteins. Mutations in members of this family, such as REP-1, lead to abnormalities, including progressive retinal degradation (choroideremia) in humans. The crystal structures of the REP-1 protein in complex with monoprenylated or C-terminally truncated Rab7 proteins revealed that Rab7 interacts with the Rab binding platform of REP-1 via an extended interface involving the Switch 1 and 2 regions. The C terminus of the REP-1 molecule functions as a mobile lid covering a conserved hydrophobic patch on the surface of REP-1 that in the complex coordinates the C terminus of Rab proteins. Using semisynthetic fluorescent Rab27A, we demonstrate that although Rab27A can be prenylated by REP-2, this reaction can be effectively inhibited by other Rab proteins, providing a possible explanation for the accumulation of unprenylated Rab27A in choroideremia.

Structure of Rab escort protein-1 in complex with Rab geranylgeranyltransferase

Posttranslational geranylgeranylation of Rab GTPases is catalyzed by Rab geranylgeranyltransferase (RabGGTase), which consists of a catalytic alpha/beta heterodimer and an accessory Rab escort protein (REP). The crystal structure of isoprenoid-bound RabGGTase complexed to REP-1 has been solved to 2.7 A resolution. The complex interface buries a surprisingly small surface area of ca. 680 A and is unexpectedly formed by helices 8, 10, and 12 of the RabGGTase alpha subunit and helices D and E of REP-1. We demonstrate that the affinity of RabGGTase for REP-1 is allosterically regulated by phosphoisoprenoid via a long-range trans-domain signal transduction event. Comparing the structure of REP-1 with the closely related RabGDI, we conclude that the specificity of the REP:RabGGTase interaction is defined by differently positioned phenylalanine residues conserved in the REP and GDI subfamilies.

Crystallization and preliminary X-ray diffraction analysis of monoprenylated Rab7 GTPase in complex with Rab escort protein 1

Posttranslational geranylgeranylation of Rab GTPases is catalyzed by Rab geranylgeranyltransferase (RabGGTase), which consists of a catalytic alpha/beta heterodimer and an accessory Rab escort protein (REP). REP functions as a molecular chaperone that presents Rab proteins to the RabGGTase and after prenylation delivers them to their target membrane. Mutations in the REP-1 gene in humans lead to an X-chromosome-linked defect known as choroideremia, a progressive disease that inevitably culminates in complete blindness. Here we report in vitro assembly, purification, and crystallization of the monoprenylated Rab7GDP:REP-1 complex. X-Ray diffraction data for the REP-1:Rab7 complex were collected to 2.2-A resolution at the ESRF. The crystals belong to the orthorhombic space group P2(1)2(1)2 with unit-cell parameters a=64.3A, b=105.3A, c=132.6A. Preliminary structural analysis revealed the presence of one complex in the asymmetric unit. To understand the conformational changes in Rab protein on complex formation we also crystallized the GDP-bound form of Rab7 that diffracted to at least 1.8A on the in-house X-ray source.

Expression of mammalian Rab Escort protein-1 and -2 in yeast Saccharomyces cerevisiae

Rab GTPases are post-translationally geranylgeranylated on their C-terminal cysteines by Rab geranylgeranyl transferase (RabGGTase) and this modification is essential for their biological activity. Rab Escort Protein (REP) is a molecular chaperone that assists in the prenylation reaction carried out by RabGGTase. Mutations in the REP-1 gene lead to progressive retinal degradation and blindness in humans. Despite the significant interest in REP proteins, their preparative production remains challenging. We report here an inducible expression system for the production of REP-1 and REP-2 in yeast Saccharomyces cerevisiae at levels 3.5 and 2mg/L, respectively. The REP-1 was found to be toxic for yeast cells and its toxicity is proposed to be associated with the formation of unproductive Ypt:REP-1 complexes. To minimize the toxic effect of REP-1, the recombinant protein expression was induced at the end of the exponential phase. Under these conditions, the GAL1 promoter is no longer repressed due to exhaustion of glucose and utilization of ethanol as a carbon source. This expression procedure was successfully scaled up to 30L for both proteins. The REP-1 and REP-2 were purified using a combination of affinity and anion-exchange chromatography. Purified proteins were functionally active, as determined by a fluorescent Rab binding assay and in vitro prenylation. The reported procedure provides a reliable source of REP proteins for biochemical and structural studies.

In vitro assembly, purification, and crystallization of the rab geranylgeranyl transferase:substrate complex

Posttranslational modification with the geranygeranyl moiety is essential for the ability of Rab GTPases to control processes of membrane docking and fusion. This modification is conferred by Rab geranylgeranyltransferase (RabGGTase), which catalyzes the transfer of two 20-carbon geranylgeranyl groups from geranylgeranyl pyrophosphate onto C-terminal cysteine residues of Rab proteins. The enzyme consists of a catalytic alpha/beta heterodimer and an accessory protein termed Rab escort protein (REP-1) that delivers the newly prenylated Rab proteins to their target membrane. In order to understand the structural basis of Rab prenylation, we have investigated in vitro assembly and crystallization of the RabGGTase:REP-1:Rab complex. In order to ensure maximal stability of the ternary complex, we generated its monoprenylated form, which corresponds to a reaction intermediate and displays the highest affinity between the components. This was achieved by expressing the individual components in baculovirus and Escherichia coli systems with subsequent purification followed by in vitro monoprenylation of Rab7 with immobilized recombinant RabGGTase. Purified monoprenylated REP-1:Rab7 was complexed with recombinant RabGGTase and crystallized in hanging drops. The crystals obtained initially diffract to 8 A on an in-house X-ray source.

Interaction of yeast Rab geranylgeranyl transferase with its protein and lipid substrates

Small GTPases from the Rab/Ypt family regulate events of vesicular traffic in eukaryotic cells. For their activity, Rab proteins require a posttranslational modification that is conferred by Rab geranylgeranyltransferase (RabGGTase), which attaches geranylgeranyl moieties onto two cysteines of their C terminus. RabGGTase is present in both lower and higher eukaryotes in the form of heterodimers composed of alpha and beta subunits. However, the alpha subunits of RabGGTases from lower eukaryotes, including Saccharomyces cerevisiae (yRabGGTase), are half the size of the corresponding subunit of the mammalian enzyme. This difference is due to the presence of additional immunoglobulin (Ig)-like and leucine rich (LRR) domains in the mammalian transferase. To understand the possible evolutionary implications and functional consequences of structural differences between RabGGTases of higher and lower eukaryotes, we have investigated the interactions of yeast RabGGTase with its lipid and protein substrate. We have demonstrated that geranylgeranyl pyrophosphate binds to the enzyme with an affinity of ca. 40 nM, while binding of farnesyl pyrophosphate is much weaker, with a K(d) value of ca. 750 nM. This finding suggests that despite the structural difference, yRabGGTase selects its lipid substrate in a fashion similar to mammalian RabGGTase. However, unlike the mammalian enzyme, yRabGGTase binds prenylated and unprenylated Ypt1p:Mrs6p complexes with similar affinities (K(d) ca. 200 nM). Moreover, in contrast to the mammalian enzyme, phosphoisoprenoids do not influence the affinity of Mrs6p for yRabGGTase. Using an in vitro prenylation assay, we have demonstrated that yRabGGTase can prenylate Rab proteins in complex with mammalian REP-1, thus indicating that neither the LRR nor the Ig-like domains, nor the recently discovered alternative pathway of catalytic complex assembly, are essential for the catalytic activity of RabGGTase. Despite the ability to function in concert with yRabGGTase in vitro, expression of mammalian REP-1 could not complement deletion of MRS6 gene in S. cerevisiae in vivo. The implications of these findings are discussed.

Double prenylation by RabGGTase can proceed without dissociation of the mono-prenylated intermediate

Rab geranylgeranyltransferase (RabGGTase) catalyzes the prenylation of Rab proteins. Despite possessing a single active site, RabGGTase is able to add geranylgeranyl moieties onto each of the two C-terminal cysteine residues of Rab. We have studied the kinetics of Rab double prenylation employing a combination of a novel high pressure liquid chromatography (HPLC)-based in vitro prenylation assay and fluorescence spectroscopy. Transfer of the first geranylgeranyl group proceeds with a k(1) = 0.16 s(-1), while the conversion from singly to double prenylated Rab is 4-fold slower (k(2) = 0.039 s(-1)). We found that following the first transfer reaction, the conjugated lipid is removed from the active site of RabGGTase but mono-prenylated Rab.REP complex remains bound to RabGGTase with a K(d) < 1 nm. In contrast to the doubly prenylated Rab7.REP dissociation of the mono-prenylated species from RabGGTase was only weakly stimulated by phosphoisoprenoid. Based on the obtained rate constants we calculated that at least 72% of mono-prenylated Rab molecules proceed to double prenylation without dissociating from RabGGTase. The obtained data provides an explanation of how RabGGTase discriminates between mono-prenylated intermediate and double prenylated reaction product. It also indicates that the phosphoisoprenoid acts both as a substrate and as a sensor governing the kinetics of protein.protein interactions in the double prenylation reaction.

Crystallization and preliminary X-ray diffraction analysis of the Rab escort protein-1 in complex with Rab geranylgeranyltransferase

Posttranslational prenylation of proteins is a widespread phenomenon and the majority of prenylated proteins are geranylgeranylated members of the Rab GTPase family. Geranylgeranylation is catalyzed by Rab geranylgeranyltransferase (RabGGTase) and is critical for the ability of Rab protein to mediate vesicular docking and fusion of various intracellular vesicles. RabGGTase consists of a catalytic alpha/beta heterodimer and an accessory protein termed Rab escort protein (REP-1) that delivers the newly prenylated Rab proteins to their target membrane. Mutations in the REP-1 gene in humans lead to an X-chromosome-linked defect known as choroideremia--a debilitating disease that inevitably culminates in complete blindness. Here we report in vitro assembly and purification of the stoichiometric ternary complex of RabGGTase with REP-1 stabilized by a hydrolysis-resistant phosphoisoprenoid analog--farnesyl phosphonyl(methyl)phoshonate. The complex formed crystals of extended plate morphology under low ionic-strength conditions. X-ray diffraction data were collected to 2.8 A resolution at the ESRF. The crystals belong to the monoclinic space group P2(1), with unit-cell parameters a = 68.7, b = 197.7, c = 86.1 A, beta = 113.4 degrees. Preliminary structural analysis revealed the presence of one molecule in the asymmetric unit.

Timing-jitter reduction in a fiber laser mode locked by an input bit stream

We present analytical and numerical results for the amount of timing-jitter reduction obtained in an all-optical clock-recovery device in which a data stream is used to mode lock a fiber laser through cross-phase modulation. This situation is analyzed when the laser pulses are close to optical solitons, so the effect of the data stream on the laser pulses is predicted from soliton perturbation theory. In our numerical simulations, both periodic input and pseudorandom input data streams are considered. The results show that for both types of data the rms timing jitter in the recovered clock is reduced significantly from that present in the input data.

Pulse propagation in nonlinear-optical fibers with phase-locked phase-sensitive amplifiers

Recently the use of periodically spaced, phase-sensitive optical parametric amplifiers was proposed for compensating for linear loss in a nonlinear fiber-optic communication line [Opt. Lett. 18, 803 (1993)]. In the previous analysis, in which the stability of a single pulse was investigated, the variation of the amplifier phases was neglected. In a physically realizable line, however, the phase of each amplifier would most likely be locked to the phase of the signal pulse or to the average of the phases of many such pulses. Here an analysis is presented in which the amplifier phase is allowed to vary in response to a signal pulse's optical phase. The analysis shows that the solitonlike signal pulses remain stable even with this additional phase variation.