Biomedical subjects

N Krauss

Publications and source records attributed to N Krauss.

At least 19 recordsLinked to original sources

PubMed2006

"Hemodynamic efficacy" of two endoscopic clip devices used in the treatment of bleeding vessels, tested in an experimental setting using the compact Erlangen Active Simulator for Interventional Endoscopy (compactEASIE) training model.

BACKGROUND AND STUDY AIMS: Hemoclip therapy is a well-established procedure in the treatment of gastrointestinal bleeding. Although new products are provided periodically by the industry, comparative investigations are lacking. We compared two different hemoclip devices in an experimental setting, assessing them using objective hemostatic parameters. MATERIALS AND METHODS: We compared two disposable clip devices (Olympus HX-200L-135 (n = 40) vs. Wilson-Cook Tri-Clip (n = 40)) in an experimental setting using the compact Erlangen Active Simulator for Interventional Endoscopy (compactEASIE) training model equipped with an upper gastrointestinal-organ package for bleeding simulation. This was a randomized, prospective, controlled trial. Four investigators with different levels of endoscopic experience applied ten hemoclip devices of each type to the spurting vessels, the clips allocated using a randomized list for each investigator. The efficacy of hemostasis was determined by continuous measurement of the pressure within the afferent vessel before and after clip application and calculation of the relative reduction of vessel diameter by the clip device. The system pressure was recorded over the period from 1 minute before to 1 minute after clip application. A secondary end point was a subjective assessment of the whole clip application procedure by the endoscopist and the assisting nurse, using a visual analog scale (0 - 100, with 100 representing the best experience). RESULTS: A total of 39/40 clips of each type were applied successfully. Both clip devices led to a significant increase in system pressure, representing significant relative reduction of vessel diameter (Olympus 5.4 +/- 7.5 %, p < 0.001; Cook 4.9 +/- 8.0 %, p < 0.001). Overall, there was no significant difference between the two devices ( P = 0.756). However, the investigator with the least experience in endoscopy (< 100 procedures) produced significantly inferior results compared with the other three investigators, who had performed between 2000 and 6000 procedures each ( P < 0.05). We found no evidence of a learning curve from the intra-observer results. The devices received good, but not significantly different, overall ratings by the endoscopists (Olympus 69 +/- 24 vs. Wilson-Cook 65 +/- 16) and by the assisting nurses (Olympus 77 +/- 9 vs. Wilson-Cook 70 +/- 22). CONCLUSIONS: Using an established cadaveric training model, no significant difference was found between the two types of hemoclip devices with respect to their "hemostatic efficacy". However, the experience of the endoscopist appears to play a major role in successful clip application. The use of a feedback mechanism in emergency endoscopy training, using continuous intravessel pressure monitoring, may substantially enhance the efficacy of training, resulting in a similar improvement in clinical results.

Cadaver↗

PubMed2005

Objective benefit of a 1-day training course in endoscopic hemostasis using the "compactEASIE" endoscopy simulator.

BACKGROUND AND STUDY AIMS: The Erlangen Active Simulator for Interventional Endoscopy (EASIE) was introduced in 1997 as a training model for interventional endoscopy. Objective evidence of the benefits of training with this model has not previously been published. As part of two long-term projects, the benefits of a 1-day training course with the "compactEASIE" simulator were evaluated. MATERIALS AND METHODS: Fourteen American and 18 French gastroenterology fellows were enrolled. These fellows were participants in the intensive groups performing training in endoscopic hemostasis, with a total number of 28 fellows in New York and 36 in France. Gastrointestinal endoscopy faculty members in New York and France evaluated and timed the fellows in four disciplines to establish baseline skills (manual skills; injection and coagulation; Hemoclip application; and variceal ligation) with the compactEASIE simulator. The trainees were reevaluated after an intensive 1-day course (with two or three fellows and one instructor per station), also including preparation and assistance for each procedure. The assessment (overall and parts) was done by expert tutors using an ordinal scale ranging from 1 to 10 (1 = poorest, 10 = best), recording also mistakes and performance time. The compactEASIE simulator, equipped with an upper gastrointestinal organ package and an artificial blood perfusion system, was used as the training tool. RESULTS: A highly significant improvement ( P < or = 0.001) was observed in the performance of all endoscopic techniques. A significant reduction in performance time was also observed with three of the four endoscopic techniques. Successful hemostasis was significantly improved in two out of three techniques. CONCLUSIONS: A 1-day training course on endoscopic hemostasis using the compactEASIE simulator is capable of improving the performance of hemostasis procedures. Long-term effects of repeated training sessions are currently subject of collaborative studies in New York and France.

Clinical Competence↗

PubMed2004

Complete remission with long-term survival in a patient with esophageal carcinoma and a tracheoesophageal fistula after treatment with the AIO regimen and bi-weekly cisplatin.

INTRODUCTION: To date, only few reports are available on patients with esophageal carcinoma containing a tracheoesophageal fistula under chemotherapy. CASE REPORT: A 56-year-old patient presented to the hospital with a stenosing squamous cell carcinoma of the esophagus containing a tracheoesophageal fistula 3 cm above the carina. After placement of a Port-a-Cath and adequate hydration he received weekly 500 mg/m (2) i. v. folinic acid (FA) as a 1 - 2-hour infusion and 2000 mg/m (2) 5-fluorouracil (5-FU) as a 24-hour infusion (24-h inf.) (AIO regimen) with prior application of bi-weekly 50 mg/m (2) i. v. cisplatin. A tracheal Y-Dumont metallic stent was inserted prior to initiating systemic treatment. The patient's alimentation was completely parenteral. After three cycles of chemotherapy (six months) the patient revealed complete remission (CR) with closure of the tracheoesophageal fistula. The tracheal Y-Dumont stent could be removed and the patient had oral alimentation restored. 29 months after initiating treatment he is without evidence of disease. CONCLUSION: Patients with esophageal carcinoma containing a tracheoesophageal fistula might benefit from chemotherapy and should not be generally excluded from systemic treatment.

Antineoplastic Agents↗

PubMed2001

Structure of photosystem I.

In plants and cyanobacteria, the primary step in oxygenic photosynthesis, the light induced charge separation, is driven by two large membrane intrinsic protein complexes, the photosystems I and II. Photosystem I catalyses the light driven electron transfer from plastocyanin/cytochrome c(6) on the lumenal side of the membrane to ferredoxin/flavodoxin at the stromal side by a chain of electron carriers. Photosystem I of Synechococcus elongatus consists of 12 protein subunits, 96 chlorophyll a molecules, 22 carotenoids, three [4Fe4S] clusters and two phylloquinones. Furthermore, it has been discovered that four lipids are intrinsic components of photosystem I. Photosystem I exists as a trimer in the native membrane with a molecular mass of 1068 kDa for the whole complex. The X-ray structure of photosystem I at a resolution of 2.5 A shows the location of the individual subunits and cofactors and provides new information on the protein-cofactor interactions. [P. Jordan, P. Fromme, H.T. Witt, O. Klukas, W. Saenger, N. Krauss, Nature 411 (2001) 909-917]. In this review, biochemical data and results of biophysical investigations are discussed with respect to the X-ray crystallographic structure in order to give an overview of the structure and function of this large membrane protein.

Crystallography, X-Ray↗

PubMed2001

Three-dimensional structure of cyanobacterial photosystem I at 2.5 A resolution.

Life on Earth depends on photosynthesis, the conversion of light energy from the Sun to chemical energy. In plants, green algae and cyanobacteria, this process is driven by the cooperation of two large protein-cofactor complexes, photosystems I and II, which are located in the thylakoid photosynthetic membranes. The crystal structure of photosystem I from the thermophilic cyanobacterium Synechococcus elongatus described here provides a picture at atomic detail of 12 protein subunits and 127 cofactors comprising 96 chlorophylls, 2 phylloquinones, 3 Fe4S4 clusters, 22 carotenoids, 4 lipids, a putative Ca2+ ion and 201 water molecules. The structural information on the proteins and cofactors and their interactions provides a basis for understanding how the high efficiency of photosystem I in light capturing and electron transfer is achieved.

Carotenoids↗

PubMed2001

Crystal structure of photosystem II from Synechococcus elongatus at 3.8 A resolution.

Oxygenic photosynthesis is the principal energy converter on earth. It is driven by photosystems I and II, two large protein-cofactor complexes located in the thylakoid membrane and acting in series. In photosystem II, water is oxidized; this event provides the overall process with the necessary electrons and protons, and the atmosphere with oxygen. To date, structural information on the architecture of the complex has been provided by electron microscopy of intact, active photosystem II at 15-30 A resolution, and by electron crystallography on two-dimensional crystals of D1-D2-CP47 photosystem II fragments without water oxidizing activity at 8 A resolution. Here we describe the X-ray structure of photosystem II on the basis of crystals fully active in water oxidation. The structure shows how protein subunits and cofactors are spatially organized. The larger subunits are assigned and the locations and orientations of the cofactors are defined. We also provide new information on the position, size and shape of the manganese cluster, which catalyzes water oxidation.

Chlorophyll↗

PubMed2001

17beta-estradiol, gender independently, reduces atheroma development but not neointimal proliferation after balloon injury in the rabbit aorta.

The aim of the present study was to investigate anti-proliferative and anti-atherogenic properties of 17beta-estradiol in balloon injured female and male rabbit aortae. Thirty-two female and 32 male New Zealand White rabbits where gonadectomised. Vascular injury was performed with a balloon catheter in the lower abdominal aorta. Male and female rabbits were randomised into four groups of eight animals each. Only two of four groups received a 0.5% cholesterol-enriched diet. One cholesterol-diet group and one normal-diet group received intramuscular injections of estradiol valerate (1 mg/kg body weight/week). After 28 days, the denuded part of the abdominal aorta was excised and analysed by morphometry and immunohistochemistry. Estrogen treatment did not show an inhibitory effect on neointimal proliferation in normo-cholesterolemic male or female rabbits. A gender independent inhibitory effect of 17beta-estradiol was seen on atheroma development in cholesterol-fed female and male rabbits, while plasma total cholesterol levels were significantly reduced in male rabbits only. The 17beta-estradiol treatment was associated with a significantly decreased number of luminal endothelial cells in normo and hyper-cholesterolemic female rabbits, as evaluated by immunohistochemical staining for 'von Willebrand factor'. Staining for Ki-67-positive proliferating cells after 28 days showed a statistically significant increased proliferative activity in the neointima of hyper-cholesterolemic female rabbits. The neointimal content of macrophages increased significantly in all hyper-cholesterolemic rabbits. Under 17beta-estradiol treatment, the number of macrophages was increased in female and decreased in male rabbits by tendency. Additionally, the 'classical' vascular estrogen receptor was present in both female and male rabbit aortae without statistically significant differences. In conclusion, 17beta-estradiol did not reduce post-injury neointima formation in normo-cholesterolemic rabbits. However, in hyper-cholesterolemic rabbits, 17beta-estradiol reduced atheroma development gender independently. This effect cannot be explained by lowering of plasma cholesterol levels or endothelium-mediated pathways, and requires further investigation on, for example, antioxidative, antiproliferative or estrogen receptor mediated effects.

Actins↗

PubMed1999

V-Amylose at atomic resolution: X-ray structure of a cycloamylose with 26 glucose residues (cyclomaltohexaicosaose).

The amylose fraction of starch occurs in double-helical A- and B-amyloses and the single-helical V-amylose. The latter contains a channel-like central cavity that is able to include molecules, "iodine's blue" being the best-known representative. Molecular models of these amylose forms have been deduced by solid state 13C cross-polarization/magic angle spinning NMR and by x-ray fiber and electron diffraction combined with computer-aided modeling. They remain uncertain, however, as no structure at atomic resolution is available. We report here the crystal structure of a hydrated cycloamylose containing 26 glucose residues (cyclomaltohexaicosaose, CA26), which has been determined by real/reciprocal space recycling starting from randomly positioned atoms or from an oriented diglucose fragment. This structure provides conclusive evidence for the structure of V-amylose, as the macrocycle of CA26 is folded into two short left-handed V-amylose helices in antiparallel arrangement and related by twofold rotational pseudosymmetry. In the V-helices, all glucose residues are in syn orientation, forming systematic interglucose O(3)n...O(2)(n+l) and O(6)n...O(2)(n+6)/O(3)(n+6) hydrogen bonds; the central cavities of the V-helices are filled by disordered water molecules. The folding of the CA26 macrocycle is characterized by typical "band-flips" in which diametrically opposed glucose residues are in anti rather than in the common syn orientation, this conformation being stabilized by interglucose three-center hydrogen bonds with O(3)n as donor and O(5)(n+l), O(6)(n+l) as acceptors. The structure of CA26 permitted construction of an idealized V-amylose helix, and the band-flip motif explains why V-amylose crystallizes readily and may be packed tightly in seeds.

Carbohydrate Conformation↗

PubMed1999

Photosystem I, an improved model of the stromal subunits PsaC, PsaD, and PsaE.

An improved electron density map of photosystem I (PSI) calculated at 4-A resolution yields a more detailed structural model of the stromal subunits PsaC, PsaD, and PsaE than previously reported. The NMR structure of the subunit PsaE of PSI from Synechococcus sp. PCC7002 (Falzone, C. J., Kao, Y.-H., Zhao, J., Bryant, D. A., and Lecomte, J. T. J. (1994) Biochemistry 33, 6052-6062) has been used as a model to interpret the region of the electron density map corresponding to this subunit. The spatial orientation with respect to other subunits is described as well as the possible interactions between the stromal subunits. A first model of PsaD consisting of a four-stranded beta-sheet and an alpha-helix is suggested, indicating that this subunit partly shields PsaC from the stromal side. In addition to the improvements on the stromal subunits, the structural model of the membrane-integral region of PSI is also extended. The current electron density map allows the identification of the N and C termini of the subunits PsaA and PsaB. The 11-transmembrane alpha-helices of these subunits can now be assigned uniquely to the hydrophobic segments identified by hydrophobicity analyses.

Amino Acid Sequence↗

PubMed1999

Case managers' and clients' perspectives on a representative payee program.

OBJECTIVE: Clients with severe and persistent mental illnesses often require a representative payee to help manage benefit funds. This study compared the perceptions of clients and clinical case managers about the benefits of and problems with the representative payee relationship. METHODS: Fifty-four clients receiving assertive community treatment completed an interview that assessed satisfaction with their experience of having a representative payee and the resulting impact on their substance use, budgeting, and housing. The clients' clinical case managers completed a similar questionnaire. Analyses examined associations between providers' and clients' responses and clients' gender, race, diagnosis, previous experience with a representative payee, and duration of the current representative payeeship. RESULTS: Clients and case managers recognized benefits of the representative payeeship in the areas of housing, substance use, and budgeting. Although little evidence was found that the payeeship pervasively interfered with the therapeutic relationship, 44 percent of case managers reported incidents in which clients verbally abused them over management of their funds. Clients' satisfaction with the representative payeeship was initially low but grew over time. Longer duration of the current payeeship and clients' previous experience with representative payeeship were associated with greater satisfaction and fewer problems. Case managers overestimated clients' initial satisfaction and underestimated their current satisfaction. CONCLUSIONS: Findings suggest that both mental health professionals and clients value the representative payee process as helpful in improving outcomes, although the benefits of the arrangement may be more evident with time and experience.

Case Management↗

PubMed1998

A common ancestor for oxygenic and anoxygenic photosynthetic systems: a comparison based on the structural model of photosystem I.

The 4 A structural model of photosystem I (PSI) has elucidated essential features of this protein complex. Inter alia, it demonstrates that the core proteins of PSI, PsaA and PsaB each consist of an N-terminal antenna-binding domain, and a C-terminal reaction center (RC)-domain. A comparison of the RC-domain of PSI and the photosynthetic RC of purple bacteria (PbRC), reveals significantly analogous structures. This provides the structural support for the hypothesis that the two RC-types (I and II) share a common evolutionary origin. Apart from a similar set of constituent cofactors of the electron transfer system, the analogous features include a comparable cofactor arrangement and a corresponding secondary structure motif of the RC-cores. Despite these analogies, significant differences are evident, particularly as regards the distances between and the orientation of individual cofactors, and the length and orientation of alpha-helices. Inferred roles of conserved amino acids are discussed for PSI, photosystem II (PSII), photosystem C (PSC, green sulfur bacteria) and photosystem H (PSH, heliobacteria). Significant sequence homology between the N-terminal, antenna-binding domains of the core proteins of type-I RCs, PsaA, PsaB, PscA and PshA (of PSI, PSC and PSH respectively) with the antenna-binding subunits CP43 and CP47 of PSII indicate that PSII has a modular structure comparable to that of PSI.

Amino Acid Sequence↗

PubMed1998

Crystal structure of human arylsulfatase A: the aldehyde function and the metal ion at the active site suggest a novel mechanism for sulfate ester hydrolysis.

Human lysosomal arylsulfatase A (ASA) is a prototype member of the sulfatase family. These enzymes require the posttranslational oxidation of the -CH2SH group of a conserved cysteine to an aldehyde, yielding a formylglycine. Without this modification sulfatases are catalytically inactive, as revealed by a lysosomal storage disorder known as multiple sulfatase deficiency. The 2.1 A resolution X-ray crystal structure shows an ASA homooctamer composed of a tetramer of dimers, (alpha 2)4. The alpha/beta fold of the monomer has significant structural analogy to another hydrolytic enzyme, the alkaline phosphatase, and superposition of these two structures shows that the active centers are located in largely identical positions. The functionally essential formylglycine is located in a positively charged pocket and acts as ligand to an octahedrally coordinated metal ion interpreted as Mg2+. The electron density at the formylglycine suggests the presence of a 2-fold disordered aldehyde group with the possible contribution of an aldehyde hydrate, -CH(OH)2, with gem-hydroxyl groups. In the proposed catalytic mechanism, the aldehyde accepts a water molecule to form a hydrate. One of the two hydroxyl groups hydrolyzes the substrate sulfate ester via a transesterification step, resulting in a covalent intermediate. The second hydroxyl serves to eliminate sulfate under inversion of configuration through C-O cleavage and reformation of the aldehyde. This study provides the structural basis for understanding a novel mechanism of ester hydrolysis and explains the functional importance of the unusually modified amino acid.

Aldehydes↗

PubMed1998

The participation of families of homeless persons with severe mental illness in an outreach intervention.

OBJECTIVES: This study describes how an Assertive Community Treatment (ACT) team which employs a family outreach worker (FOW) interacts with homeless persons with severe mental illness and their families. METHODS: The team's ratings of the frequency and importance of clients' and treatment team's family contact are summarized and compared with independent research reports on patients' satisfaction with family relations, housing and hospitalization outcomes. RESULTS: 73% of clients had contact with their families. ACT worked with families of 61% of clients. ACT had less contact with the families of men (p < .01) and substance abusers (p < .01). Client days in stable housing were associated with increased ACT family contact (p < .05). CONCLUSIONS: Most ACT clients had significant family contact. ACT established contact with most families, and the work with families appeared to be associated with higher levels of satisfaction with family relations and housing. The role of the FOW should be explored further.

Adult↗

PubMed1997

Photosystem I of Synechococcus elongatus at 4 A resolution: comprehensive structure analysis.

An improved structural model of the photosystem I complex from the thermophilic cyanobacterium Synechococcus elongatus is described at 4 A resolution. This represents the most complete model of a photosystem presently available, uniting both a photosynthetic reaction centre domain and a core antenna system. Most constituent elements of the electron transfer system have been located and their relative centre-to-centre distances determined at an accuracy of approximately 1 A. These include three pseudosymmetric pairs of Chla and three iron-sulphur centres, FX, FA and FB. The first pair, a Chla dimer, has been assigned to the primary electron donor P700. One or both Chla of the second pair, eC2 and eC'2, presumably functionally link P700 to the corresponding Chla of the third pair, eC3 and eC'3, which is assumed to constitute the spectroscopically-identified primary electron acceptor(s), A0, of PSI. A likely location of the subsequent phylloquinone electron acceptor, QK, in relation to the properties of the spectroscopically identified electron acceptor A1 is discussed. The positions of a total of 89 Chla, 83 of which constitute the core antenna system, are presented. The maximal centre-to-centre distance between antenna Chla is < or = 16 A; 81 Chla are grouped into four clusters comprising 21, 23, 17 and 20 Chla, respectively. Two "connecting" Chla are positioned to structurally (and possibly functionally) link the Chla of the core antenna to those of the electron transfer system. Thus the second and third Chla pairs of the electron transfer system may have a dual function both in energy transfer and electron transport. A total of 34 transmembrane and nine surface alpha-helices have been identified and assigned to the 11 subunits of the PSI complex. The connectivity of the nine C-terminal (seven transmembrane, two "surface") alpha-helices of each of the large core subunits PsaA and PsaB is described. The assignment of the amino acid sequence to the transmembrane alpha-helices is proposed and likely residues involved in co-ordinating the Chla of the electron transfer system discussed.

Bacterial Proteins↗

PubMed1997

The structural organization of the PsaC protein in Photosystem I from single crystal EPR and X-ray crystallographic studies.

In Photosystem I (PS I) the terminal electron acceptors, FA and FB, are iron-sulfur (4Fe-4S) centers, which are bound to the stromal subunit PsaC. The orientation of PsaC is determined relative to the whole PS I complex (see Schubert, W.-D. et al. (1995) in From Light to Biosphere (Mathis, P. ed.), Vol. II, pp. 3-10, Kluwer) from which a molecular model for the structure of PsaC within PS I is derived. Two strategies are followed: (i) PS I single crystal EPR data on the orientation of the g tensors of both FA- and FB- relative to each other and relative to the crystal axes (see preceding paper) are used in conjunction with the central structural part of the bacterial 2 [Fe4S4] ferredoxins, the cysteine binding motifs of which are known to be homologous to those of PsaC; (ii) the same core structure is fitted into the intermediate resolution electron density map of PS I. The PsaC orientation obtained both ways agree well. The local twofold symmetry axis inherent to the ferredoxin model leaves a twofold ambiguity in the structural conclusion. Deviations from this C2-symmetry in the amino acid sequence of PsaC are analyzed with respect to observable properties which would resolve the remaining structural ambiguity. Arguments both for and against FA being the distal iron-sulfur center (to FX) are discussed.

Amino Acid Sequence↗

PubMed1996

Photosystem I at 4 A resolution represents the first structural model of a joint photosynthetic reaction centre and core antenna system.

The 4 A X-ray structure model of trimeric photosystem I of the cyanobacterium Synechococcus elongatus reveals 31 transmembrane, nine surface and three stromal alpha-helices per monomer, assigned to the 11 protein subunits: PsaA and PsaB are related by a pseudo two-fold axis normal to the membrane plane, along which the electron transfer pigments are arranged. 65 antenna chlorophyll a (Chl a) molecules separated by < or = 16 A form an oval, clustered net continuous with the electron transfer chain through the second and third Chl a pairs of the electron transfer system. This suggests a dual role for these Chl a both in excitation energy and electron transfer. The architecture of the protein core indicates quinone and iron-sulphur type reaction centres to have a common ancestor.

Cell Membrane↗

PubMed1995

Modifying the PACT model to serve homeless persons with severe mental illness.

The success of the Program for Assertive Community Treatment (PACT) has led to its replication with different client populations, especially those who are underserved by the traditional treatment system. This paper describes a program in Baltimore that has adapted the PACT model to serve homeless persons with severe mental illness. Although the essential ingredients and philosophy of the original model were maintained, the original team approach has been modified by the use of "miniteams." All staff share knowledge of all program clients through formal mechanisms such as daily meetings; however, each client is assigned to a miniteam composed of a clinical case manager, a psychiatrist, and a consumer advocate. Another deviation from the PACT model is that services can be time limited. The authors describe four phases of treatment and problems, including interventions characteristic of each phase.

Adult↗

PubMed1994

Crystal structure of beta-D-cellotetraose hemihydrate with implications for the structure of cellulose II.

The crystal structure of beta-D-cellotetraose shows the same molecule packing as cellulose II, with two antiparallel molecules in the unit cell: For cellulose II, the orientation of the C6-O6 bonds has been described as gauche-trans and trans-gauche, respectively, for the two antiparallel molecules, which otherwise have identical conformations. In contrast, in beta-D-cellotetraose all C6-O6 bonds are gauche-trans, but the conformations of the two antiparallel molecules are different. Energy minimization and molecular dynamics studies suggest that the structure of cellulose II should be reinvestigated in light of these findings.

Carbohydrate Conformation↗