Biomedical subjects

B Westermann

Publications and source records attributed to B Westermann.

At least 19 recordsLinked to original sources

PubMed2000

SNAREpins are functionally resistant to disruption by NSF and alphaSNAP.

SNARE (SNAP [soluble NSF (N-ethylmaleimide-sensitive fusion protein) attachment protein] receptor) proteins are required for many fusion processes, and recent studies of isolated SNARE proteins reveal that they are inherently capable of fusing lipid bilayers. Cis-SNARE complexes (formed when vesicle SNAREs [v-SNAREs] and target membrane SNAREs [t-SNAREs] combine in the same membrane) are disrupted by the action of the abundant cytoplasmic ATPase NSF, which is necessary to maintain a supply of uncombined v- and t-SNAREs for fusion in cells. Fusion is mediated by these same SNARE proteins, forming trans-SNARE complexes between membranes. This raises an important question: why doesn't NSF disrupt these SNARE complexes as well, preventing fusion from occurring at all? Here, we report several lines of evidence that demonstrate that SNAREpins (trans-SNARE complexes) are in fact functionally resistant to NSF, and they become so at the moment they form and commit to fusion. This elegant design allows fusion to proceed locally in the face of an overall environment that massively favors SNARE disruption.

Adenosine Triphosphate↗

PubMed2000

Mitochondria-targeted green fluorescent proteins: convenient tools for the study of organelle biogenesis in Saccharomyces cerevisiae.

We describe the construction and characterization of a novel set of plasmids for expression of mitochondria-targeted green fluorescent protein (GFP) in Saccharomyces cerevisiae. The vectors include constructs with strong regulatable and constitutive promoters, four different auxotrophic markers for yeast transformation, and a green (S65T) and a blue-shifted (P4-3) variant of GFP. Mitochondria are brightly fluorescent in living yeast cells grown on different carbon sources and at different temperatures, with virtually no background staining. Specific staining of mitochondria is also shown for a respiratory-deficient mutant with abnormal mitochondrial morphology. The plasmids facilitate convenient analysis of mutants defective in mitochondrial morphology or inheritance and, at the same time, are suitable vectors for easy construction of different kinds of GFP fusion proteins to study various aspects of organelle biogenesis in living yeast cells.

Cloning, Molecular↗

PubMed2000

Online head motion tracking applied to the patient registration problem.

Image-guided systems for surgical procedures in the region of the head require a method to correlate the diagnostic image data with the corresponding site of pathology in the patient. Considering that patient movement can occur, detection and correction of such movement errors during the acquisition of images is a basic prerequisite for accurate treatment. For this reason, we developed a new registration method based upon on-line tracking of the patient's head to solve the problem of registration in the presence of head motion. The method provides non-invasive active patient registration for correction of movements during imaging and continuous update of the patient's head position during surgery. The patient motion correction applies the rigid body model to register the images using feature correspondence. The new registration method is described, and results of experiments that were performed to evaluate its accuracy and reliability in a plastic skull model and in patients are presented. The error analysis resulted in a final target registration error of 0.90 mm +/- 0.16 mm using experimental model data and 1.58 mm +/- 0.26 mm using clinical patient data. In addition, the residual registration error is modeled as a function of the measured and predicted head motion in order to determine the error that is introduced by motion tracking during image data acquisition. Furthermore, the clinical application of the method is demonstrated for oto-, rhino-, and neurosurgical procedures in the region of the head.

Algorithms↗

PubMed2000

Hemocyanin re-uptake in the renal and branchial heart appendages of the coleoid cephalopod Sepia officinalis.

The renal and branchial heart appendages of Sepia officinalis L. were investigated in order to elucidate a possible involvement of their excretory epithelia in hemocyanin metabolism. Immunocytochemical findings and tracer experiments indicate that after passing the barrier of ultrafiltration the hemocyanin molecules are taken up by the epithelial cells of the renal and branchial heart appendages and are subsequently carried back to the circulatory system, suggesting a mechanism of hemocyanin recycling. Apart from a function in maintaining constant hemocyanin levels, the present study indicates that the renal and branchial heart appendages are also sites of temporary hemocyanin storage.

Animals↗

PubMed2000

Tracer studies of food absorption in the digestive tract of Nautilus pompilius (Cephalopoda, Tetrabranchiata).

In Nautilus pompilius, tracer experiments with 14C-labelled food show that the midgut gland, caecum and crop are involved in absorption of nutrients. According to liquid scintillation and light- and electron-microscopic autoradiography, the midgut gland exhibits the highest activity, followed by the caecum and crop. The density of silver precipitates is highest in the terminal alveoli of the midgut gland. Precipitates are also seen in the main cells of the caecal epithelium. Few precipitates are found in the lamina epithelialis mucosae of the crop, indicating that, in addition to food storage, digestive processes begin in this organ. These results have been confirmed by injection of the protein ferritin into the buccal cavity. The largest amount of ferritin is seen in the dense bodies of the main cells of the midgut gland, whereas those of the main cells of the caecum and crop contain less ferritin.

Animals↗

PubMed2000

Role of MMM1 in maintaining mitochondrial morphology in Neurospora crassa.

Mmm1p is a protein required for maintenance of mitochondrial morphology in budding yeast. It was proposed that it is required to mediate the interaction of the mitochondrial outer membrane with the actin cytoskeleton. We report the cloning and characterization of MMM1 of the filamentous fungus Neurospora crassa, an organism that uses microtubules for mitochondrial transport. Mutation of the mmm-1 gene leads to a temperature-sensitive slow growth phenotype and female sterility. Mutant cells harbor abnormal giant mitochondria at all stages of the asexual life cycle, whereas actin filament-depolymerizing drugs have no effect on mitochondrial morphology. The MMM1 protein has a single transmembrane domain near the N terminus and exposes a large C-terminal domain to the cytosol. The protein can be imported into the outer membrane in a receptor-dependent manner. Our findings suggest that MMM1 is a factor of general importance for mitochondrial morphology independent of the cytoskeletal system used for mitochondrial transport.

Amino Acid Sequence↗

PubMed1999

Diastereoselective Synthesis of C-Glycosylated Amino Acids with Lactams as Peptide Building Blocks.

Readily available by lipase-catalyzed kinetic resolution or from a chiral pool, beta-, gamma-, and delta-lactams can be used as peptide building blocks for the synthesis of C-glycosylated amino acids 1. By reaction with glycosyl dianions, metabolic stable glycosylated amino acids can be prepared diastereoselectively. Ac=acetyl; Bn=benzyl; Boc=tert-butoxycarbonyl; R=Et, Bn; R'=H, alkyl; n=1-3.

Journal Article↗

PubMed1999

Rapid and efficient fusion of phospholipid vesicles by the alpha-helical core of a SNARE complex in the absence of an N-terminal regulatory domain.

A protease-resistant core domain of the neuronal SNARE complex consists of an alpha-helical bundle similar to the proposed fusogenic core of viral fusion proteins [Skehel, J. J. & Wiley, D. C. (1998) Cell 95, 871-874]. We find that the isolated core of a SNARE complex efficiently fuses artificial bilayers and does so faster than full length SNAREs. Unexpectedly, a dramatic increase in speed results from removal of the N-terminal domain of the t-SNARE syntaxin, which does not affect the rate of assembly of v-t SNARES. In the absence of this negative regulatory domain, the half-time for fusion of an entire population of lipid vesicles by isolated SNARE cores ( approximately 10 min) is compatible with the kinetics of fusion in many cell types.

Lipid Bilayers↗

PubMed1999

Dual role of the mitochondrial chaperone Mdj1p in inheritance of mitochondrial DNA in yeast.

Mdj1p, a homolog of the bacterial DnaJ chaperone protein, plays an essential role in the biogenesis of functional mitochondria in the yeast Saccharomyces cerevisiae. We analyzed the role of Mdj1p in the inheritance of mitochondrial DNA (mtDNA). Mitochondrial genomes were rapidly lost in a temperature-sensitive mdj1 mutant under nonpermissive conditions. The activity of mtDNA polymerase was severely reduced in the absence of functional Mdj1p at a nonpermissive temperature, demonstrating the dependence of the enzyme on Mdj1p. At a permissive temperature, the activity of mtDNA polymerase was not affected by the absence of Mdj1p. However, under these conditions, intact [rho(+)] genomes were rapidly converted to nonfunctional [rho(-)] genomes which were stably propagated in an mdj1 deletion strain. We propose that mtDNA polymerase depends on Mdj1p as a chaperone in order to acquire and/or maintain an active conformation at an elevated temperature. In addition, Mdj1p is required for the inheritance of intact mitochondrial genomes at a temperature supporting optimal growth; this second function appears to be unrelated to the function of Mdj1p in maintaining mtDNA polymerase activity.

DNA, Fungal↗

PubMed1999

Optical tracking of a microscope for image-guided intranasal sinus surgery.

The objective of this study was to examine the effects of optical and tracking properties on the accuracy of an optically locatable operating microscope. The intraoperative arrangement was based on experimental results obtained from a skull model. Measurements were taken from 24 patients undergoing intranasal microscopic sinus surgery for various disorders. Two major groups of influencing factors were determined from measurements on the model: 1) optical properties of the microscope, such as the method of focal point adjustment, focal length, and magnification of the lens; and 2) tracking properties of the microscope, such as the distance of the digitizer to the tracked object, the number of reference infrared light-emitting diodes (IR-LEDs), and the area circumscribed by these IR-LEDs. Patient measurements showed an overall spatial error of 2.39+/-1.15 mm with a laser-supported adjustment of the focal point of the microscope. Although the associated 95th percentile was at 4.36 mm, such a value is encouraging for further development of microscopically navigable systems. It must be noted that the noninvasive patient-to-image registration was performed on the basis of a computed tomographic image with a slice distance of 2 mm.

Electronic Data Processing↗

PubMed1998

Fzo1p is a mitochondrial outer membrane protein essential for the biogenesis of functional mitochondria in Saccharomyces cerevisiae.

Fzo1p is a novel component required for the biogenesis of functional mitochondria in the yeast Saccharomyces cerevisiae. The protein is homologous to Drosophila Fzo, the first known protein mediator of mitochondrial fusion. Deletion of the FZO1 gene results in a petite phenotype, loss of mitochondrial DNA, and a fragmented mitochondrial morphology. Fzo1p is an integral protein of the mitochondrial outer membrane exposing its major part to the cytosol. It is imported into the outer membrane in a receptor-dependent manner. Fzo1p is part of a larger protein complex of 800 kDa, and presumably is the first identified component of the yeast mitochondrial fusion machinery.

Fungal Proteins↗

PubMed1998

SNAREpins: minimal machinery for membrane fusion.

Recombinant v- and t-SNARE proteins reconstituted into separate lipid bilayer vesicles assemble into SNAREpins-SNARE complexes linking two membranes. This leads to spontaneous fusion of the docked membranes at physiological temperature. Docked unfused intermediates can accumulate at lower temperatures and can fuse when brought to physiological temperature. A supply of unassembled v- and t-SNAREs is needed for these intermediates to form, but not for the fusion that follows. These data imply that SNAREpins are the minimal machinery for cellular membrane fusion.

Bacterial Proteins↗

PubMed1998

Cytobiological studies on hemocyanin metabolism in the branchial heart complex of the common cuttlefish Sepia officinalis (Cephalopoda, Dibranchiata).

The present study confirms previous investigations that demonstrated a high copper content in the branchial heart and its appendage, and that gave the first indication that this organ complex might be involved in hemocyanin metabolism in Sepia officinalis L. Immunocytochemical localization of hemocyanin molecules within the endocytotic lysosomal system of the ovoid cells and tracer experiments with 125I-labeled Sepia hemocyanin suggest its endocytotic uptake. Energy-dispersive X-ray microanalysis and histochemical methods reveal a high copper content within the ovoid cells of the branchial heart. In view of the turnover of the respiratory pigment in the branchial heart of Sepia officinalis L., we believe that the ovoid cells are a site of hemocyanin catabolism.

Animals↗

PubMed1998

Cytological and enzyme-histochemical investigations on the digestive organs of Nautilus pompilius (Cephalopoda, Tetrabranchiata).

The foregut, stomach, caecum, midgut, and rectum of the digestive tract of Nautilus pompilius L.were investigated with ultrastructural and enzyme-cytological methods. Three different cell types were identified within the lamina epithelialis mucosae: main cells, goblet cells, and cells with secretory granules. The main cell type is the epithelial cell with microvilli, a basal nucleus surrounded by dictyosomes, rough endoplasmic reticulum, mitochondria, and electron-dense granules identified as lysosomes in the apical part of the cell. In the caecum this cell type contains endosymbiotic bacteria. The presence of endocytotic vesicles and the storage of lipids in the caecum indicate that this organ is involved in the process of absorption. In the caecum and the longitudinal groove of the rectum the main cells are, in addition, ciliated, facilitating the transport of food particles and faeces. Two types of goblet cells are found in all organs except in the stomach, forming a gliding path for food particles and protecting the epithelium. In the foregut and rectum, cells with electron-dense granules were recognized as the third type. The conspicuous secretory cells of the rectum represent a delimited rectal gland; its possible biological function is discussed. The tunica muscularis in all organs of the digestive tract consists of obliquely striated muscle cells innervated by axons containing transparent, osmiophilic and dense-cored vesicles. Positive reactions for acid and alkaline phosphatase, monoamine oxidase, beta-glucuronidase, and trypsin- and chymotrypsin-like enzymes are localized in the lamina epithelialis mucosae.

Animals↗

PubMed1997

Mdj2p, a novel DnaJ homolog in the mitochondrial inner membrane of the yeast Saccharomyces cerevisiae.

Members of the heat shock protein 70 (Hsp70) family mediate import, folding, assembly and degradation of proteins in mitochondria. The function of Hsp70 proteins is dependent on their interaction with cofactors, including members of the DnaJ protein family. The mitochondrial DnaJ homolog, Mdj1p, has been shown to cooperate with the major mitochondrial Hsp70, mt-Hsp70. We describe the identification of a second mitochondrial DnaJ homolog, Mdj2p, in the yeast Saccharomyces cerevisiae. The protein possesses an N-terminal transmembrane domain that anchors it in the mitochondrial inner membrane. The C-terminal J-domain shares 30% amino acid identity with the J-domain of Escherichia coli DnaJ and is exposed to the mitochondrial matrix. Mdj2p carries a putative internal mitochondrial targeting signal and is imported into mitochondria in a membrane potential-dependent manner. Deletion of the MDJ2 gene did not result in a detectable growth defect. Double mutants of mdj1 and mdj2 showed severe growth defects at elevated temperature, indicating a distinct overlap of the functions of Mdj1p and Mdj2p.

Amino Acid Sequence↗

PubMed1997

Noninvasive tracking of patient's head movements during computer-assisted intranasal microscopic surgery.

A noninvasive system designed for patient tracking during image-guided intranasal sinus surgery is described. It is based on optical digitizing with a custom-made registration and reference system, locatable surgical instruments, and a self-localizing operating microscope. Experimental and clinical results reveal a high degree of accuracy for the system. A mean spatial error of 0.82 +/- 0.31 mm was determined for repositioning of the reference system in a plastic model of the skull. For the positioning of the microscope, a mean error of 2.3 +/- 0.83 mm was calculated. Measurements of repositioning accuracy in 24 patients who received surgery for various sinus diseases had a mean spatial error of 1.56 +/- 0.76 mm. The 95% error interval for locating intranasal structures using the surgical instrument was 2.05 mm, and it was 4.92 mm using the microscope. These results suggest that the use of our noninvasive registration and reference system may be effective, accurate, and useful for noninvasive tracking of patient movements in computer-assisted intranasal surgery.

Head Movements↗

PubMed1997

A non-invasive patient registration and reference system for interactive intraoperative localization in intranasal sinus surgery.

A basic problem common to all systems for computer assisted surgery (CAS) is patient referencing, or the transfer of preoperative image data to the intraoperative pathology. The authors describe a highly precise CAS system with non-invasive referencing that can be used in ear, nose and throat (ENT) surgery of the paranasal sinuses. It is based on optical digitizing with several custom-made self-localizing surgical instruments. The accuracy of the system was tested in an experimental model using a plastic head. Measurements of repositioning the reference bow had a mean error of 0.81 mm +/- 0.31 mm. The system was evaluated clinically with 11 patients who received surgery for different pathologies of the paranasal sinuses. These trials met with a high rate of success and specific results are reported.

Biopsy↗

PubMed1996

The nucleotide exchange factor MGE exerts a key function in the ATP-dependent cycle of mt-Hsp70-Tim44 interaction driving mitochondrial protein import.

Import of preproteins into the mitochondrial matrix is driven by the ATP-dependent interaction of mt-Hsp70 with the peripheral inner membrane import protein Tim44 and the preprotein in transit. We show that Mge1p, a co-chaperone of mt-Hsp70, plays a key role in the ATP-dependent import reaction cycle in yeast. Our data suggest a cycle in which the mt-Hsp70-Tim44 complex forms with ATP: Mge1p promotes assembly of the complex in the presence of ATP. Hydrolysis of ATP by mt-Hsp70 occurs in complex with Tim44. Mge1p is then required for the dissociation of the ADP form of mt-Hsp70 from Tim44 after release of inorganic phosphate but before release of ADP. ATP hydrolysis and complex dissociation are accompanied by tight binding of mt-Hsp70 to the preprotein in transit. Subsequently, the release of mt-Hsp70 from the polypeptide chain is triggered by Mge1p which promotes release of ADP from mt-Hsp70. Rebinding of ATP to mt-Hsp70 completes the reaction cycle.

Adenosine Triphosphate↗