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Biomedical subjects

P Markiewicz

Publications and source records attributed to P Markiewicz.

At least 19 recordsLinked to original sources
PubMed2001

[Treatment of intracranial aneurysms during pregnancy].

Aneurysmal subarachnoid hemorrhage (SAH) during pregnancy is rare but serious obstetric complication. SAH occurs more often in primiparae and in the third trimester of pregnancy. The hemodynamic and endocrine changes play an important role in the growth and rupture of aneurysms. There are no differences in the clinical course of SAH among pregnant and non-pregnant patients. Subarachnoid hemorrhage during pregnancy may be confused with eclampsia. The confirmation of the diagnosis is made by computed tomography (CT) or lumbar puncture and cerebral angiography. Ruptured intracranial aneurysms should be treated as they would be in patients who are not pregnant. When the aneurysm is successfully clipped, the pregnancy can be allowed to progress to term. In these cases the vaginal delivery is preferred by most clinicians. Caesarean section would be indicated in several circumstances: when the clinical state of mother is severe (coma, brain stem damage), if the aneurysm is diagnosed at term of labour, if the interval between the neurosurgical treatment of aneurysm and labour is less than 8 days.

Adult↗
PubMed2001

[The application and evaluation of TachoComb in repair of lacerations of dural sac].

The opening of dural sac (deliberate or accidental) during operation of the spine should be watertightly closed because of the risk of cerebro-spinal fluid leakage and infectious complications. Suturing the dural sac is sometimes difficult and time-consuming in cases of dural sac lacerations in a narrow confined space or in the proximity of radices. This occurs particularly in the case of reoperation in presence of scar involving the dural sac, that increases the risk of laceration. The aim of this paper is to asses the usefulness of a new sealing and haemostatic material--TachoComb in a watertight closure of the dural sac during spinal operation. We compared the frequency of complications related to closing of the dural sac in patients operated before and after introduction of TachoComb. The results indicate that the rate of liquorrhoea and infections is lower in the postoperative period with addition of TachoComb. Addition of TachoComb allows to shorten the time of operation, while its application is relatively easy.

Adolescent↗
PubMed2001

Cardiopulmonary manifestations of subarachnoid hemorrhage--a case report.

The study presents a case of a 48-year-old female patient, in whom first symptoms of subarachnoid hemorrhage were suggestive of acute pulmonary oedema, caused by acute left ventricular insufficiency, evoked by myocardial infarction. The authors discuss the course of illness, diagnostic difficulties and changes in circulatory system, which can appear as a result of subarachnoid hemorrhage.

Cardiovascular Diseases↗
PubMed1997

Lac repressor genetic map in real space.

Here, we present a graphic display of the phenotypes of more than 4000 single amino acid substitution mutations on the three-dimensional structure of the lac repressor tetramer bound to DNA. The genetic data and the X-ray diffraction studies contribute to define an allosteric mechanism and yield a visual demonstration of the importance of core or buried residues in protein structure.

Allosteric Site↗
PubMed1997

Paired helical filaments are twisted ribbons composed of two parallel and aligned components: image reconstruction and modeling of filament structure using atomic force microscopy.

To study the structure of Alzheimer paired helical filaments (PHF) we examined isolated detergent-insoluble PHF using atomic force microscopy with image reconstruction. The reconstructed AFM images of Alzheimer PHF most closely resembled ribbon-like helices with thin edges. The presence of a conspicuous furrow in the PHF midline indicated that PHF were composed of two distinctive strands. Our present conception of the overall configuration of PHF is consistent with that proposed by Crowther and Wischik in 1985 but includes an essential component of the prevailing model: the presence of two strands. Thus, our new model of PHF structure, based on atomic force microscopy-derived data, indicates that the true structure of PHF is actually a hybrid of the prevailing PHF model and a thin helical ribbon.

Alzheimer Disease↗
PubMed1997

[Theories of intracranial aneurysm etiology].

The main theories of the origin of intracranial aneurysms as the most common vascular malformations are presented. Three main theories maintain that they are either the congenital, acquire or both of those defects. The presence of aneurysms in the bifurcations of the arteries with the loss of the muscle layer and the coexistence with other vascular malformations of the arteries and their rareness in children give the evidence of the acquire origin. The present theories join this two positions and take into consideration also the hemodynamic and inflammation as well as degeneration, atheromatosis, toxic and traumatic factors.

Hemodynamics↗
PubMed1996

Genomic and cDNA sequence tags of the hyperthermophilic archaeon Pyrobaculum aerophilum.

The hyperthermophilic archaeum, Pyrobaculum aerophilum, grows optimally at 100 degrees C with a doubling time of 180 min. It is a member of the phylogenetically ancient Thermoproteales order, but differs significantly from all other members by its facultatively aerobic metabolism. Due to its simple cultivation requirements and its nearly 100% plating efficiency, it was chosen as a model organism for studying the genome organization of hyperthermophilic ancient archaea. By a G+C content of the DNA of 52 mol%, sequence analysis was easily possible. At least some of the mRNA of P. aerophilum carried poly-A tails facilitating the construction of a cDNA library. 245 sequence tags of a poly-A primed cDNA library and 55 sequence tags from a 1-2 kb Sau3AI-fragment containing genomic library were analyzed and the corresponding amino acid sequences compared with protein sequences from databases. Fourteen percent of the cDNA and >9% of genomic DNA sequence tags revealed significant similarities to proteins in the databases. Matches were obtained to proteins from archaeal, bacterial and eukaryal sources. Some sequences showed greatest similarity to eukaryal rather than to bacterial versions of proteins, other matches were found to proteins which had previously only been found in eukaryotes.

Archaea↗
PubMed1996

Genetic studies of the Lac repressor. XV: 4000 single amino acid substitutions and analysis of the resulting phenotypes on the basis of the protein structure.

Each amino acid from position 2 to 329 of Lac repressor was replaced by 12 or 13 of the 20 natural occurring amino acids. The resulting phenotypes are discussed on the basis of (1) the recently published structure of the Lac repressor core complexed with the inducer IPTG and (2) a model of the dimeric Lac repressor built by homology modelling from the X-ray structure of the purine repressor-corepressor-operator complex. This phenotype analysis, based on 4000 well-defined mutants, yields a functional description of each amino acid position of Lac repressor. In most cases, mutant effects can be directly correlated with the structure and function of the protein. This connection between the amino acid position and the structure and function of the protein is in most cases direct and not complicated: amino acids which are directly involved in sugar binding are affected in Lac repressor mutants of the Is type; small amino acids which can only be replaced by other small acids are located in the core of the protein; positions at which nearly all amino acids are tolerated are in most cases located on the surface of the protein. Amino acids which are highly conserved throughout the LacI family of repressors, and not directly involved in specific functions of the protein like DNA recognition or sugar binding, form a network of contacts with other amino acids. Such amino acids are either located inside one subunit, mostly at the interface between secondary structure elements, or are involved in the dimerisation interface.

Amino Acid Sequence↗
PubMed1996

E. coli SSB activates N4 virion RNA polymerase promoters by stabilizing a DNA hairpin required for promoter recognition.

Bacteriophage N4 virion RNA polymerase transcription of double-stranded promoter-containing DNAs requires supercoiled template and E. coli single-stranded DNA-binding protein (EcoSSB); other single-stranded DNA-binding proteins cannot substitute. The DNA determinants of virion RNA polymerase binding at the promoter comprise a small template-strand hairpin. The requirement for EcoSSB is surprising, since single-stranded DNA-binding proteins destabilize hairpin structures. DNA footprinting of EcoSSB on wild-type and mutant promoters indicates that EcoSSB stabilizes the template-strand hairpin owing to the hairpin-loop sequences. Other single-stranded DNA-binding proteins destabilize the promoter hairpin, explaining the specificity of EcoSSB activation. We conclude that EcoSSB activates transcription by providing the appropriate DNA structure for polymerase binding. The existence of small hairpins stable to single-stranded protein binding suggests a novel mechanism that provides structural determinants for specific recognition in single-stranded DNA transactions by an otherwise nonspecific DNA-binding protein.

Base Sequence↗
PubMed1995

Alzheimer paired helical filaments: a comparison with the twisted ribbon model.

To investigate if Alzheimer paired helical filaments (PHF) closely resemble twisted ribbons, as indicated by recent high-resolution ultrastructural studies, we compared physical models of twisted ribbons with electron microscopic images of PHF. Uranyl-acetate-stained, isolated PHF with one or two helical turns were compared with scale models of twisted ribbons with one and two helical turns rotated at different angles. The various rotations of the twisted ribbon model corresponded well with the different orientations of randomly dispersed PHF. The electron-dense regions of individual PHF turns previously thought to represent a cross-over site of paired filaments corresponded to the edge of the twisted ribbon when the ribbon was oriented perpendicular to the filament axis. These data indicate that the overall configuration of PHF is a twisted ribbon but does not exclude possible configuration restrictions due to an ordered arrangement of subunits.

Alzheimer Disease↗
PubMed1995

Sequential assembly of collagen revealed by atomic force microscopy.

Most polymers which comprise biological filaments assemble by two mechanisms: nucleation and elongation or a sequential, stepwise process involving a hierarchy of intermediate species. We report the application of atomic force microscopy (AFM) to the study of the early events in the sequential or stepwise mode of assembly of a macromolecular filament. Collagen monomers were assembled in vitro and the early structural intermediates of the assembly process were examined by AFM and correlated with turbidimetric alterations in the assembly mixture. The assembly of collagen involved a sequence of distinctive filamentous species which increased in both diameter and length over the time course of assembly. The first discrete population of collagen oligomers were 1-2 nm in diameter (300-500 nm in length); at later time points, filaments approximately 2-6 nm in diameter (> 10 microns in length) many with a conspicuous approximately 67-nm axial period were observed. Occasional mature collagen fibrils with a approximately 67-nm axial repeat were found late in the course of assembly. Our results are consistent with initial end-to-end axial association of monomers to form oligomers followed by lateral association into higher-order filaments. On this basis, there appears to be at least two distinctive types of structural interactions (axial and lateral) which are operative at different levels in the assembly hierarchy of collagen.

Animals↗
PubMed1994

Identification and sequencing of the Thermotoga maritima lacZ gene, part of a divergently transcribed operon.

The lacZ gene encoding a beta-galactosidase (beta Gal) from the hyperthermophile Thermotoga maritima was cloned on an 11-kb fragment by complementation of an Escherichia coli lacZ deletion stain. The nucleotide sequence of the structural gene and two other ORFs found within a 6317-bp region were determined. The deduced amino acid (aa) sequence of the Tt. maritima beta Gal predicts a 1037-aa polypeptide with a calculated M(r) of 122,312. The translated sequence is 30% similar to nine other beta Gal sequences from bacteria and one yeast. Alignment of the Tt. maritima beta Gal with these other sequences reveals that the residues responsible for Mg2+ binding, catalysis and substrate recognition are conserved in the thermophilic enzyme. Sequence analysis also revealed the presence of a divergently transcribed operon containing at least two other genes 5' to lacZ. These ORFs encode proteins homologous to a second family of beta Gal found in Bacillus species and to an ATP-dependent family of bacterial oligopeptide transport proteins.

Amino Acid Sequence↗
PubMed1994

Genetic studies of the lac repressor. XIV. Analysis of 4000 altered Escherichia coli lac repressors reveals essential and non-essential residues, as well as "spacers" which do not require a specific sequence.

Amber mutations have been constructed at 328 positions, corresponding to residues 2 to 329 in the E. coli lac repressor protein. Synthetic and naturally occurring nonsense suppressors have been used to insert, in series, 12-13 amino acids at positions specified by an amber (UAG) codon in the lacI mRNA. The resulting set of over 4000 single amino acid replacements in the lac repressor protein allows a detailed analysis of its substitution tolerance along the linear array of residues, and reveals structure-function relationships in lac repressor and in proteins in general. (1) There are two main regions in the repressor which are extremely sensitive to amino acid replacements. One, the amino-terminal 59 residues, has been implicated in DNA and operator binding by a large body of work. The second, extending from approximately residues 239 to 289/292, forms the repressor core and shares the most homology with other repressor and DNA binding proteins. (2) Throughout the rest of the protein, segments of 6 to 14 amino acids, which are highly tolerant to single amino acid replacements, appear to act as "spacers" between one or several hydrophobic residues that are relatively intolerant to substitutions. (3) We have replaced the amino acids in these tolerant regions with spans of alanine residues, from 5 to 13 amino acids. In all five of the regions tested, alanine replacements, sometimes of up to 8 amino acids, still allowed functional repressor, while deletion of the same residues destroyed repressor function. This reinforces the view that many regions of a protein do not require a specific sequence to serve as spacers between more important residues. (4) A distinct pattern of substitutions leading to the I(s) phenotype suggests the location of residues involved in inducer binding. (5) A number of general substitution patterns can be recognized. For instance, proline is not tolerated at over 40 sites which tolerate all the other amino acid replacements. Another set of sites tolerates only non-polar amino acids, whereas a third set tolerates a subset of the smallest amino acids, (serine, alanine, glycine and cysteine, and sometimes threonine and valine). (5) Overall, 93 of 328 sites (28%) tolerate all 13 amino acids tested, and 144 of 328 (44%) tolerate 12/13 or all 13 substitutions. We judge that 192 of 328 sites (59%) are generally tolerant to substitutions.

Alanine↗
PubMed1994

The sequence of a subtilisin-type protease (aerolysin) from the hyperthermophilic archaeum Pyrobaculum aerophilum reveals sites important to thermostability.

The hyperthermophilic archaeum Pyrobaculum aerophilum grows optimally at 100 degrees C and pH 7.0. Cell homogenates exhibit strong proteolytic activity within a temperature range of 80-130 degrees C. During an analysis of cDNA and genomic sequence tags, a genomic clone was recovered showing strong sequence homology to alkaline subtilisins of Bacillus sp. The total DNA sequence of the gene encoding the protease (named "aerolysin") was determined. Multiple sequence alignment with 15 different serine-type proteases showed greatest homology with subtilisins from gram-positive bacteria rather than archaeal or eukaryal serine proteases. Models of secondary and tertiary structure based on sequence alignments and the tertiary structures of subtilisin Carlsberg, BPN', thermitase, and protease K were generated for P. aerophilum subtilisin. This allowed identification of sites potentially contributing to the thermostability of the protein. One common transition put alanines at the beginning and end of surface alpha-helices. Aspartic acids were found at the N-terminus of several surface helices, possibly increasing stability by interacting with the helix dipole. Several of the substitutions in regions expected to form surface loops were adjacent to each other in the tertiary structure model.

Amino Acid Sequence↗
PubMed1994

Mallory body filaments become insoluble after normal assembly into intermediate filaments.

The deposition of 8-to-10-nm filaments into inclusion bodies is a fundamental cellular change that occurs in several degenerative processes of many tissues. However, little is known about the pathological filaments including whether the filaments assemble by the same mechanisms that govern the assembly of normal intermediate filaments. We have addressed this issue by studying the in vitro reassembly of the cytokeratin filaments that are deposited into experimental murine Mallory bodies (MBs) but have not yet become covalently crosslinked components of the MB. The reassembly process of both normal hepatocellular and MB-derived cytokeratins (CKs) was similar and characterized by a hierarchy of protofilament and protofibrils with a prominent axial periodicity of approximately 21 nm (normal hepatocellular CK, 20.7 +/- 2 nm; MB-derived CK, 20.1 +/- 2 nm). Purified MB-derived CK and normal hepatocellular CK comigrated in polyacrylamide gel electrophoresis indicating composition by similar CK isoforms. These results indicate that intermediate filaments formed from MB-derived CK are indistinguishable from filaments assembled from normal CK. On this basis, we conclude that the intermediate filaments that form inclusion bodies are not aberrantly assembled but become aggregated and post-translationally modified after their initial formation.

Animals↗
PubMed1994

Twisted ribbon structure of paired helical filaments revealed by atomic force microscopy.

Progressive deposition of phosphorylated tau into the paired helical filaments (PHF) that compose neurofibrillary tangles, dystrophic neurites, and neuropil threads is an obligate feature of Alzheimer's disease. The standard model of PHF structure, derived from electron microscopic studies, suggests that two 8- to 10-nm filaments each composed of three to four protofilaments are wound into a helix with a maximal diameter of -20 nm and a half period of 65 to 80 nm. However, recent vertical platinum-carbon replicas of PHF more closely resemble a thin helical ribbon without constitutive protofilaments. Here we report that native PHF imaged with an atomic force microscope appear as twisted ribbons rather than the generally accepted structure derived from electron microscopic studies. These data imply that the assembly of PHF is not due to the twisting of pair-wise filaments but rather the helical winding of self-associated tau molecules arranged into a flattened structure. Future structural models of PHF should be based on quantitative data obtained from imaging techniques, such as scanning probe microscopy, which do not require harsh specimen preparation procedures.

Alzheimer Disease↗
PubMed1993

Studies of the hyperthermophile Thermotoga maritima by random sequencing of cDNA and genomic libraries. Identification and sequencing of the trpEG (D) operon.

Random sequencing of cDNA and genomic libraries has been used to study the genome of the hyperthermophile Thermotoga maritima. To date, 175 unique clones have been analyzed by comparing short sequence tags with known proteins in the PIR and GenBank databases. We find that a significant proportion of sequences can be matched to previously identified protein from non-Thermotoga sources. A high match rate was obtained from an oligo(dT)-primed cDNA library, where one-third of all unique sequences analyzed (21/65) shared high amino acid sequence similarity with proteins in the PIR and GenBank databases. Also, approximately one-third of the unique sequences from a second cDNA library (28/89), constructed with random oligo primers, could be matched to sequences in PIR and GenBank. Identification of genes from the oligo(dT)-primed cDNA library indicates that some Thermotoga mRNAs are polyadenylated. Genes have also been identified from a 1 to 2 kb genomic DNA library. Here, (3/21) of genomic sequences analyzed could be matched to protein in PIR and GenBank. One of the genomic clones had high sequence similarity to the tryptophan synthesis gene anthranilate synthase component I (trpE). Using this sequence tag, the Thermotoga trp operon was isolated and sequenced. The Thermotoga maritima trp operon is arranged with trpE forming an overlapping transcript with a second protein consisting of a fusion of anthranilate synthase component II (trpG) and anthranilate phosphoribosyltransferse (trpD). With regard to the fusion, the operon organization is similar to Escherichia coli and Salmonella typhimurium, but lacks the classic attenuation system of enteric bacteria. Amino acid sequence comparison with 19 trpE, 18 trpG and 14 trpD genes from other organisms suggest that the Thermotoga trp genes resemble corresponding genes from other thermophiles more closely than expected.

Amino Acid Sequence↗