Biomedical subjects

Volker Müller

Publications and source records attributed to Volker Müller.

At least 19 recordsLinked to original sources

PubMed2006

Does the inactivation of leukocytes in blood transfusions during and following liver transplantation by gamma-irradiation have an impact on rejection and infection rate?

BACKGROUND: Leukocytes transmitted in blood products exert a variety of immunological side-effects. Experience with bone marrow transplant recipients has shown that these can be induced even by very few cells. In liver transplant recipients, who usually receive large amounts of blood products, the effects of transfused leukocytes with regards to the rates of rejection and infection have not yet been investigated. MATERIAL/METHODS: Twenty liver transplant recipients were prospectively randomized to receive blood products (red blood cells, thrombocytes, fresh frozen plasma) through a leukocyte depletion filter, either irradiated with 40 Gy or not irradiated (10 patients, respectively). During the observation period of 90 days, the incidences of infections and rejections were analyzed. In addition, liver function tests, markers of infection (C reactive protein, lipopolysaccharide binding protein), and subpopulations of lymphocytes (total cell count, CD4/CD8 ratio, CD8CD45RO) were determined. RESULTS: Only one episode of mild rejection occurred (irradiated group). Rates of persistent graft dysfunction and severe infections were similar in both groups. The same applied to liver function tests, parameters of infection, and subpopulations of lymphocytes. CONCLUSIONS: These preliminary results suggest that irradiation of already leukocyte-depleted blood products may not be necessary and beneficial in liver transplant recipients.

Adult↗

PubMed2006

Autoinducer-2-producing protein LuxS, a novel salt- and chloride-induced protein in the moderately halophilic bacterium Halobacillus halophilus.

The moderately halophilic bacterium Halobacillus halophilus carries a homologue of LuxS, a protein involved in the activated methyl cycle and the production of autoinducer-2, which mediates quorum sensing between certain species. luxS of H. halophilus is part of an operon that encodes an S-adenosylmethionine-dependent methyltransferase, a cysteine synthase, and a beta-cystathionine lyase. Expression of luxS was growth phase dependent, with maximal expression in the mid-exponential growth phase. In addition, transcription of luxS was strictly salt dependent; maximal mRNA concentrations were observed with 2.0 M NaCl in the growth medium. Chloride ions stimulated luxS transcription by a factor of three. Western blot analyses demonstrated a growth phase- and salinity-dependent production of LuxS. Moreover, cellular LuxS levels were strictly chloride dependent. Maximal accumulation of LuxS was observed at 0.5 to 1.0 M Cl(-) and depended on the salinity.

Amino Acid Sequence↗

PubMed2006

Structural and functional analysis of the coupling subunit F in solution and topological arrangement of the stalk domains of the methanogenic A1AO ATP synthase.

The first low-resolution shape of subunit F of the A(1)A(O) ATP synthase from the archaeon Methanosarcina mazei Gö1 in solution was determined by small angle X-ray scattering. Independent to the concentration used, the protein is monomeric and has an elongated shape, divided in a main globular part with a length of about 4.5 nm, and a hook-like domain of about 3.0 nm in length. The subunit-subunit interaction of subunit F inside the A(1)A(O) ATP synthase in the presence of 1-ethyl-3-(dimethylaminopropyl)-carbodiimide EDC was studied as a function of nucleotide binding, demonstrating movements of subunits F relative to the nucleotide-binding subunit B. Furthermore, in the intact A(1)A(O) complex, crosslinking of subunits D-E, A-H and A-B-D was obtained and the peptides, involved, were analyzed by MALDI-TOF mass spectrometry. Based on these data the surface of contact of B-F could be mapped in the high-resolution structure of subunit B of the A(1)A(O) ATP synthase.

ATP Synthetase Complexes↗

PubMed2006

Bioenergetics of archaea: ancient energy conserving mechanisms developed in the early history of life.

A key component in cellular bioenergetics is the ATP synthase. The enzyme from archaea represents a new class of ATPases, the A1AO ATP synthases. They are composed of two domains that function as a pair of rotary motors connected by a central and peripheral stalk(s). The structure of the chemically-driven motor (A1) was solved by small angle X-ray scattering in solution, and the structure of the first A1AO ATP synthases (from methanoarchaea) was obtained recently by single particle analyses. These studies revealed novel structural features such as a second peripheral stalk and a collar-like structure. Interestingly, the membrane-embedded electrically-driven motor (AO) is very different in archaea with sometimes novel, exceptional subunit composition.

Amino Acid Sequence↗

PubMed2006

Biochemical and molecular characterization of the biosynthesis of glutamine and glutamate, two major compatible solutes in the moderately halophilic bacterium Halobacillus halophilus.

The moderately halophilic, chloride-dependent bacterium Halobacillus halophilus produces glutamate and glutamine as main compatible solutes at external salinities of 1.0 to 1.5 M NaCl. The routes for the biosynthesis of these solutes and their regulation were examined. The genome contains two genes potentially encoding glutamate dehydrogenases and two genes for the small subunit of a glutamate synthase, but only one gene for the large subunit. However, the expression of these genes was not salt dependent, nor were the corresponding enzymatic activities detectable in cell extracts of cells grown at different salinities. In contrast, glutamine synthetase activity was readily detectable in H. halophilus. Induction of glutamine synthetase activity was strictly salt dependent and reached a maximum at 3.0 M NaCl; chloride stimulated the production of active enzyme by about 300%. Two potential genes encoding a glutamine synthetase, glnA1 and glnA2, were identified. The expression of glnA2 but not of glnA1 was increased up to fourfold in cells adapted to high salt, indicating that GlnA2 is the glutamine synthetase involved in the synthesis of the solutes glutamate and glutamine. Furthermore, expression of glnA2 was stimulated twofold by the presence of chloride ions. Chloride exerted an even more pronounced effect on the enzymatic activity of preformed enzyme: in the absence of chloride in the assay buffer, glutamine synthetase activity was decreased by as much as 90%. These data demonstrate for the first time a regulatory role of a component of common salt, chloride, in the biosynthesis of compatible solutes.

Bacillaceae↗

PubMed2005

Stress response by solute accumulation in archaea.

The accumulation of organic solutes is a prerequisite for osmotic adjustment of all organisms. Archaea synthesize unusual solutes such as beta-amino acids, Nepsilon-acetyl-beta-lysine, mannosylglycerate and di-myo-inositol phosphate but, as in other cells, uptake of solutes such as glycine betaine is preferred over de novo synthesis. Study of the molecular basis of osmoadaptation and its regulation in archaea is still in its infancy, but genomics and functional genome analyses combined with classical biochemistry shed light on the processes that confer osmoadaptation in archaea. Most interestingly, some solutes are not only produced in response to salt but also to temperature stress.

Amino Acids↗

PubMed2005

Arterialisation of the portal vein as a model for the induction of hepatic fibrosis: description of microsurgical models in the rat.

Within the framework of liver transplantation, arterialisation of the portal vein in the case of non-recanalisable thrombosis has been reactivated. However, one of the consequences of this vascular reconstruction is the development of hepatic fibrosis. Clinical experience has shown that the development of fibrosis can be avoided by reducing portal inflow. We present, as a model for the induction of hepatic fibrosis, techniques of PVA, including transplantation. For PVA, several different techniques were used: the first with reduction of the portal inflow over a stent inserted in the right renal artery (PVA-B), the second with unrestricted flow using an aortic-portal segment (PVA-APS). The third technique was orthotopic liver transplantation with unrestricted portal arterialisation (OLTx-APS). Portal blood flow was measured with an ultrasonic flow probe. To determine the degree of hepatic fibrosis the amount of hydroxyproline was measured. Quantification of relative transcript levels of procollagen I was effected with real-time PCR using the TaqMan technology on a lightcycler instrument. The extracellular matrix was visualised with picro-sirius staining. Measurements with the ultrasonic probe showed a significant increase in flow rates, both with reduced (PVA-B) and unrestricted inflow (PVA-APS; OLTx-APS). The lowest survival rate (58%) was found in the group with unrestricted portal inflow. The reason for this was a high rate of thrombosis in the in the portal vascular tree (4 out of 12). In the OLTx-APS group four animals died within the first 3 postoperative days (69%), as a result of protracted postoperative shock. The overall survival rate was the highest (85%) in the group undergoing PVA with reduction of the portal inflow. PVA with unrestricted inflow was followed by a significant increase in extracellular collagen, which showed a clear correlation with the increase in the amount of hydroxyproline, the level of the mRNA for procollagen I and picro-sirius staining. With the operative PVA techniques presented herein, different arterial flow rates in the portal vein can be investigated. In our opinion these techniques represent an excellent animal model for studying the genesis of fibrosis and antifibrotic substances. By regulating the blood flow in the arterialised portal vein hepatic fibrosis can be reduced or even avoided. After a brief period of learning the microsurgical techniques, the surgeon can limit clamping times and achieve good results with these techniques.

Animals↗

PubMed2005

ATP synthases with novel rotor subunits: new insights into structure, function and evolution of ATPases.

ATPases with unusual membrane-embedded rotor subunits were found in both F(1)F(0) and A(1)A(0) ATP synthases. The rotor subunit c of A(1)A(0) ATPases is, in most cases, similar to subunit c from F(0). Surprisingly, multiplied c subunits with four, six, or even 26 transmembrane spans have been found in some archaea and these multiplication events were sometimes accompanied by loss of the ion-translocating group. Nevertheless, these enzymes are still active as ATP synthases. A duplicated c subunit with only one ion-translocating group was found along with "normal" F(0) c subunits in the Na(+) F(1)F(0) ATP synthase of the bacterium Acetobacterium woodii. These extraordinary features and exceptional structural and functional variability in the rotor of ATP synthases may have arisen as an adaptation to different cellular needs and the extreme physicochemical conditions in the early history of life.

Acetobacterium↗

PubMed2005

Successful treatment of hepatitis C reinfection with interferon-alpha2b and ribavirin after liver transplantation.

INTRODUCTION: Recurrence of hepatitis C virus (HCV) infection after orthotopic liver transplantation (OLT) is a virtually universal occurrence, and a significant proportion of patients develop chronic hepatitis and cirrhosis. The aim of this study was to evaluate the safety and efficacy of interferon (IFN)-alpha2b plus ribavirin (RIBA) in the treatment of recurrent HCV after OLT over the long term. MATERIAL AND METHODS: Fifteen patients with recurrent HCV infection (positive serum HCV RNA, elevated serum aminotransferases, histological activity) were started on IFN-alpha2b (3-6 million units administered subcutaneously three times a week) plus RIBA (800-1200 mg/day) 18+/-5 months after OLT. HCV RNA was determined 1, 3, 6, 9, 12 and 18 months after initiation of treatment. Liver biopsy was performed before and after therapy. The patients were followed up for a mean of 33+/-5 months. RESULTS: Thirteen patients (87%) were treated for at least 6 months and nine patients (60%) for 12 months. After 3 months, 11 patients (73%) were free from HCV RNA (<50 copies/ml); the virological end-of-treatment response was 67%. Five patients (33%) remained HCV RNA-negative 6 months posttreatment (sustained response (SR)). During the follow-up period, four patients (27%) died of liver failure, recurrent HCV after virological response, or HCC. The histological activity index improved significantly for both inflammatory activity and fibrosis, from 8.8 to 4.7 and from 7.3 to 4.8, respectively. In none of the patients were signs of rejection observed. CONCLUSION: Combination therapy with IFN and RIBA in transplanted patients with chronic hepatitis C is an effective treatment that results in a high virological SR rate. It is well tolerated and leads to an improvement in histological outcome.

Adult↗

PubMed2004

Effects of portal vein arterialization on regeneration and morphology in liver transplantation: investigations using the rat model.

BACKGROUND: Portal vein arterialization (PVA) has been proposed as a technical variant in liver transplantation in the case of non-recanalizable thrombosis. The present study investigates the effects of the arterialized portal vein on the function, morphology, and regenerative behavior of the liver. METHODS: Different PVA techniques, including orthotopic liver transplantation, were used in a rat model. Portal blood flow was measured using a ultrasonic flowmeter. The regeneration capacity was determined on the basis of the increase of liver weight and the proliferating cell nuclear antigen index. The amount of hydroxyproline and the transcript levels of procollagen I were measured to determine the degree of fibrosis. The extracellular matrix was visualized with Picro-Sirius staining. RESULTS: The measurements obtained with an ultrasonic probe revealed a significant increase in portal blood flow after PVA. The regeneration capacity in the groups after PVA with no flow reduction was comparable to that of the control. Liver transplantation and PVA with no flow reduction was followed by a significant increase (four- to sixfold) in the amount of hydroxyproline and the level of the mRNA for procollagen I. In the Picro-Sirius staining, periportal and perivascular fibrosis with incipient formation of septa was seen. After reduction of the portal blood flow, these effects were significantly less pronounced. CONCLUSIONS: These operative techniques represent an excellent small animal model for studying the mechanism of liver regeneration and the genesis of fibrosis in liver and vessel tissue. The presenting findings indicate that the negative effects of "overarterialization" may be largely avoided by reducing portal blood flow. This implies that permanent PVA in clinical liver transplantation should be performed only in conjunction with a down-regulation of portal flow.

Alanine Transaminase↗

PubMed2004

The evolution of A-, F-, and V-type ATP synthases and ATPases: reversals in function and changes in the H+/ATP coupling ratio.

Members of the FoF1, AoA1 and VoV1 family of ATP synthases and ATPases have undergone at least two reversals in primary function. The first was from a progenitor proton-pumping ATPase to a proton-driven ATP synthase. The second involved transforming the synthase back into a proton-pumping ATPase. As proposed earlier [FEBS Lett. 259 (1990) 227], these reversals required changes in the H+/ATP coupling ratio from an optimal value of about 2 for an ATPase function to about 4 for an ATP synthase function. The doubling of the ratio that occurred at the ATPase-to-Synthase transition was accomplished by duplicating the gene that encodes the nucleotide-binding catalytic subunits followed by loss of function in one of the genes. The halving of the ratio that occurred at the Synthase-to-ATPase transition was achieved by a duplication/fusion of the gene that encodes the proton-binding transporter subunits, followed by a loss of function in one half of the double-sized protein. These events allowed conservation of quaternary structure, while maintaining a sufficient driving force to sustain an adequate phosphorylation potential or electrochemical gradient. Here, we describe intermediate evolutionary steps and a fine-tuning of the H+/ATP coupling ratio to optimize synthase function in response to different environments. In addition, we propose a third reversal of function, from an ATPase back to an ATP synthase. In contrast to the first two reversals which required a partial loss in function, the change in coupling ratio required for the third reversal is explained by a gain in function.

Adenosine Triphosphatases↗

PubMed2004

Structure and subunit arrangement of the A-type ATP synthase complex from the archaeon Methanococcus jannaschii visualized by electron microscopy.

In Archaea, bacteria, and eukarya, ATP provides metabolic energy for energy-dependent processes. It is synthesized by enzymes known as A-type or F-type ATP synthase, which are the smallest rotatory engines in nature (Yoshida, M., Muneyuki, E., and Hisabori, T. (2001) Nat. Rev. Mol. Cell. Biol. 2, 669-677; Imamura, H., Nakano, M., Noji, H., Muneyuki, E., Ohkuma, S., Yoshida, M., and Yokoyama, K. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 2312-2315). Here, we report the first projected structure of an intact A(1)A(0) ATP synthase from Methanococcus jannaschii as determined by electron microscopy and single particle analysis at a resolution of 1.8 nm. The enzyme with an overall length of 25.9 nm is organized in an A(1) headpiece (9.4 x 11.5 nm) and a membrane domain, A(0) (6.4 x 10.6 nm), which are linked by a central stalk with a length of approximately 8 nm. A part of the central stalk is surrounded by a horizontal-situated rodlike structure ("collar"), which interacts with a peripheral stalk extending from the A(0) domain up to the top of the A(1) portion, and a second structure connecting the collar structure with A(1). Superposition of the three-dimensional reconstruction and the solution structure of the A(1) complex from Methanosarcina mazei Gö1 have allowed the projections to be interpreted as the A(1) headpiece, a central and the peripheral stalk, and the integral A(0) domain. Finally, the structural organization of the A(1)A(0) complex is discussed in terms of the structural relationship to the related motors, F(1)F(0) ATP synthase and V(1)V(0) ATPases.

ATP Synthetase Complexes↗

PubMed2004

Three-dimensional organization of the archaeal A1-ATPase from Methanosarcina mazei Gö1.

A modified isolation procedure provides a homogeneous A(1)-ATPase from the archaeon Methanosarcina mazei Gö1, containing the five subunits in stoichiometric amounts of A(3):B(3):C:D:F. A(1) obtained in this way was characterized by three-dimensional electron microscopy of single particles, resulting in the first three-dimensional reconstruction of an A(1)-ATPase at a resolution of 3.2 nm. The A(1) consists of a headpiece of 10.2 nm in diameter and 10.8 nm in height, formed by the six elongated subunits A(3) and B(3). At the bottom of the A(3)B(3) complex, a stalk of 3.0 nm in length can be seen. The A(3)B(3) domain surrounds a large cavity that extends throughout the length of the A(3)B(3) barrel. A part of the stalk penetrates inside this cavity and is displaced toward an A-B-A triplet. To investigate further the topology of the stalk subunits C-F in A(1), cross-linking has been carried out by using dithiobis[sulfosuccinimidylpropionate] (DSP) and 1-ethyl-3-(dimethylaminopropyl)-carbodiimide (EDC). In experiments where DSP was added the cross-linked products B-F, A(x)-D, A-B-D, and A(x)-B(x)-D were formed. Subunits B-F, A-D, A-B-D, and A-B-C-D could be cross-linked by EDC. The subunit-subunit interaction in the presence of DSP was also studied as a function of nucleotide binding, demonstrating movements of subunits C, D, and F during ATP cleavage. Finally, the three-dimensional organization of this A(1) complex is discussed in terms of the relationship to the F(1)- and V(1)-ATPases at a resolution of 3.2 nm.

Adenosine Triphosphatases↗

PubMed2004

An exceptional variability in the motor of archael A1A0 ATPases: from multimeric to monomeric rotors comprising 6-13 ion binding sites.

The motor domain of A1A0 ATPases is composed of only two subunits, the stator subunit I and the rotor subunit c. Recent studies on the molecular biology of the A0 domains revealed the surprising finding that the gene encoding subunit c underwent several multiplication events leading to rotor subunits comprising 2, 3, or even 13 hairpin domains suggesting multimeric in different stoichiometry as well as monomeric rotors. The number of ion translocating groups per rotor ranges from 13 to 6. Furthermore, as deduced from the gene sequences H(+)-as well as Na(+)-driven rotors are found in archaea. Features previously thought to be distinctive for A0, F0 or V0 are all found in A0 suggesting that the differences encountered in the three classes of ATPases today emerged already very early in evolution. The extraordinary features and exceptional structural and functional variability in the rotor of A1A0 ATPases may have arisen as an adaptation to different cellular needs and the extreme physicochemical conditions in the early history of life.

Archaea↗

PubMed2003

Impact of changing immunosuppressive monotherapy from Cyclosporin A to Tacrolimus in long-term, stable liver transplant recipients.

A number of studies have reported a lower atherogenic lipid profile in liver transplant recipients under tacrolimus (FK506) than in those under cyclosporine A (CyA) immunosuppression. This has mainly been attributed to the steroid-saving effect of FK506. However, the effects of converting CyA to FK506 monotherapy on lipid metabolism have not been specifically investigated. In 20 patients with stable graft function, immunosuppressive monotherapy was switched from CyA to FK506 because of CyA-related side-effects (hypertension, nephrotoxicity, hypercholesterolaemia). Serum lipid levels were measured before and 3, 6 and 12 months after conversion. In 5 patients, a modification of immunosuppression became necessary during the study period (4 were reconverted to CyA, 1 to glucocorticoids). In the remaining 15 patients on FK506 monotherapy, 12 months after conversion, a slight decrease in mean serum cholesterol, a slight increase in LDL, but a significant decrease in mean serum HDL were observed, resulting in a significant increase in Chol/HDL and LDL/HDL ratios. Conversion of immunosuppressive monotherapy from CyA to FK506 had no beneficial effect on the atherogenic lipid profile in this selected study population of long-term liver transplant survivors.

Arteriosclerosis↗

PubMed2003

Chloride dependence of growth in bacteria.

Chloride is an abundant anion on earth but studies analyzing a possible function of chloride in prokaryotes are scarce. To address the question, we have tested 44 different Gram-negative and Gram-positive bacteria for a chloride dependence or chloride stimulation of growth. None required chloride for growth at their optimal growth (salt) conditions. However, in hyperosmotic media containing high concentrations of Na+, 11 bacteria (Aeromonas hydrophila, Bacillus megaterium, Bacillus subtilis, Corynebacterium glutamicum, Escherichia coli, Paracoccus denitrificans, Proteus mirabilis, Proteus vulgaris, Staphylococcus aureus, Thermus thermophilus, and Vibrio fischeri) had a strict chloride dependence for growth or were significantly stimulated by chloride. These data show that chloride is essential for growth at high salt (Na+) concentrations in various species of the domain Bacteria.

Chlorides↗

PubMed2003

Coexistence of group I and group II chaperonins in the archaeon Methanosarcina mazei.

Two distantly related classes of cylindrical chaperonin complexes assist in the folding of newly synthesized and stress-denatured proteins in an ATP-dependent manner. Group I chaperonins are thought to be restricted to the cytosol of bacteria and to mitochondria and chloroplasts, whereas the group II chaperonins are found in the archaeal and eukaryotic cytosol. Here we show that members of the archaeal genus Methanosarcina co-express both the complete group I (GroEL/GroES) and group II (thermosome/prefoldin) chaperonin systems in their cytosol. These mesophilic archaea have acquired between 20 and 35% of their genes by lateral gene transfer from bacteria. In Methanosarcina mazei Gö1, both chaperonins are similarly abundant and are moderately induced under heat stress. The M. mazei GroEL/GroES proteins have the structural features of their bacterial counterparts. The thermosome contains three paralogous subunits, alpha, beta, and gamma, which assemble preferentially at a molar ratio of 2:1:1. As shown in vitro, the assembly reaction is dependent on ATP/Mg2+ or ADP/Mg2+ and the regulatory role of the beta subunit. The co-existence of both chaperonin systems in the same cellular compartment suggests the Methanosarcina species as useful model systems in studying the differential substrate specificity of the group I and II chaperonins and in elucidating how newly synthesized proteins are sorted from the ribosome to the proper chaperonin for folding.

Adenosine Triphosphatases↗

PubMed2003

Defined subcomplexes of the A1 ATPase from the archaeon Methanosarcina mazei Gö1: biochemical properties and redox regulation.

The potential A(1) ATPase genes ahaA, ahaB, ahaC, ahaD, ahaE, ahaF, and ahaG from the anaerobic archaeon Methanosarcina mazei Gö1 were overexpressed in Escherichia coli DK8 (pTL2). An A(1) complex was purified to apparent homogeneity and shown by Western blot and N-terminal sequence analyses to contain subunits A, B, C, D, and F but to be devoid of subunits E and G. Further removal of subunit C was without effect on ATPase activity. The enzyme was most active at pH 5.2 and required bisulfite and acetate for maximal activity. Kinetic studies confirmed three new inhibitors for A(1) ATPases (diethylstilbestrol and its derivatives hexestrol and dienestrol) and identified redox modulation as a new type of regulation of archaeal A(1) ATPases.

Adenosine Triphosphatases↗