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K P Schäfer

Publications and source records attributed to K P Schäfer.

At least 19 recordsLinked to original sources
PubMed2001

Overexpression and purification of Helicobacter pylori flavodoxin and induction of a specific antiserum in rabbits.

Flavodoxin from the gastric pathogen Helicobacter pylori has been shown to be the electron acceptor of the essential pyruvate-oxidoreductase enzyme complex and proposed to be involved in the pathogenesis of gastric MALToma. In order to obtain a sufficient amount for biochemical and structural studies, we overexpressed the protein either with a C-terminal His(6) -tag or as a fusion protein upstream of intein- and chitin-binding domains. With both expression systems we succeeded at purifying soluble and functional flavodoxin containing the cofactor FMN. When expressing with a His(6) -tag, we purified approximately 20 mg flavodoxin per liter of bacterial culture, while expression as an intein-CBD fusion protein with autocatalytic removal of the intein-CBD part rendered only approximately 1 mg of purified flavodoxin per liter of bacterial culture. Expressed as an intein-CBD fusion protein, flavodoxin copurified with a C-terminal degradation product, which was not observed for expression with a His(6) -tag. However, we were able to obtain protein crystals suited for X-ray structure determination from flavodoxin expressed as an intein-CBD fusion protein, but not from flavodoxin expressed with a C-terminal His(6) -tag. We further report the induction of a rabbit antiserum specific for H. pylori flavodoxin.

Animals↗
PubMed2001

Mutations of the Helicobacter pylori genes rdxA and pbp1 cause resistance against metronidazole and amoxicillin.

To investigate amoxicillin and metronidazole resistance of Helicobacter pylori, we compared putative resistance genes between resistant strains obtained in vitro and their sensitive parent strain. All metronidazole-resistant strains had rdxA mutations, and an amoxicillin-resistant strain had pbp1 and pbp2 mutations. By transforming PCR products of these mutated genes into antibiotic-sensitive strains, we showed that rdxA null mutations were sufficient for metronidazole resistance, while pbp1 mutations contributed to amoxicillin resistance of H. pylori.

Amino Acid Sequence↗
PubMed1999

Helicobacter pylori cadA encodes an essential Cd(II)-Zn(II)-Co(II) resistance factor influencing urease activity.

Inactivation of Helicobacter pylori cadA, encoding a putative transition metal ATPase, was only possible in one of four natural competent H. pylori strains, designated 69A. All tested cadA mutants showed increased growth sensitivity to Cd(II) and Zn(II). In addition, some of them showed both reduced 63Ni accumulation during growth and no or impaired urease activity, which was not due to lack of urease enzyme subunits. Gene complementation experiments with plasmid (pY178)-derived H. pylori cadA failed to correct the deficiencies, whereas resistance to Cd(II) and Zn(II) was restored. Moreover, pY178 conferred increased Co(II) resistance to both the cadA mutants and the wild-type strain 69A. Heterologous expression of H. pylori cadA in an Escherichia coli zntA mutant resulted in an elevated resistance to Cd(II) and Zn(II). Expression of cadA in E. coli SE5000 harbouring H. pylori nixA, which encodes a divalent cation importer along with the H. pylori urease gene cluster, led to about a threefold increase in urease activity compared with E. coli control cells lacking the H. pylori cadA gene. These results suggest that H. pylori CadA is an essential resistance pump with ion specificity towards Cd(II), Zn(II) and Co(II). They also point to a possible role of H. pylori CadA in high-level activity of H. pylori urease, an enzyme sensitive to a variety of metal ions.

Adenosine Triphosphatases↗
PubMed1998

Molecular characterization of metal-binding polypeptide domains by electrospray ionization mass spectrometry and metal chelate affinity chromatography.

Metal ion-binding of synthetic peptides containing HxH and CxxC motifs was investigated by electrospray ionization mass spectrometry (ESI-MS) and metal chelate affinity chromatography. A high affinity of Ni2+ and Cu2+ to HxH containing sequences was found. Based on their natural metal ion-binding potential it was possible to include metal affinity chromatography in the purification process of two proteins without using an additional His-tag sequence: ATPase-439, a P type ATPase from Helicobacter pylori and the amyloid precursor protein (APP).

Adenosine Triphosphatases↗
PubMed1998

Synthesis and structural characterization of human-identical lung surfactant SP-C protein.

An efficient synthesis for human-identical lung surfactant protein SP-C is described with a semi-automated solid phase synthesizer using Fmoc chemistry. Double coupling and acetic anhydride capping procedures were employed for synthetic cycles within the highly hydrophobic C-terminal domain of SP-C. Isolation of the protein was performed by mild cleavage and deprotection conditions and subsequent HPLC purification yielding a highly homogeneous protein as established by sequence determination, electrospray, plasma desorption and MALDI mass spectrometry. A general method has been employed for the preparation of Cys-palmitoylated protein by using temporary Cys(tButhio) protection, in situ deprotection with beta-mercaptoethanol and selective palmitoylation of resin-bound SP-C. The mild synthesis and isolation conditions provide SP-C with a high alpha-helical content, comparable to that of the natural SP-C, as assessed by CD spectra. Furthermore, first biophysical data indicate a surfactant activity comparable to that of the natural protein.

Amino Acid Sequence↗
PubMed1998

The Helicobacter felis ftsH gene encoding an ATP-dependent metalloprotease can replace the Escherichia coli homologue for growth and phage lambda lysogenization.

Cloning and sequencing of an approximately 6.0-kb chromosomal DNA fragment from Helicobacter felis revealed five complete open reading frames. The deduced amino acid sequence of one ORF exhibited sequence similarity to the FtsH protein, an ATP-dependent metalloprotease, from various bacterial species. The encoded protein consists of 638 amino acid residues with a molecular mass of 70.2 kDa. The hydropathy profile of the FtsH protein predicted two N-terminal transmembrane regions that were confirmed experimentally. Insertion of ftsH into a new versatile expression vector resulted in overexpression of FtsH protein in Escherichia coli. In addition, the E. coli ftsH gene could be replaced by the H. felis homologue to allow reduced growth and tenfold increased lysogenization by temperate phage lambda.

ATP-Dependent Proteases↗
PubMed1998

Properties of the P-type ATPases encoded by the copAP operons of Helicobacter pylori and Helicobacter felis.

The cop operons of Helicobacter pylori and Helicobacter felis were cloned by gene library screening. Both operons contain open reading frames for a P-type ion pump (CopA) with homology to Cd2+ and Cu2+ ATPases and a putative ion binding protein (CopP), the latter representing a CopZ homolog of the copYZAB operon of Enterococcus hirae. The predicted CopA ATPases contained an N-terminal GMXCXXC ion binding motif and a membrane-associated CPC sequence. A synthetic N-terminal peptide of the H. pylori CopA ATPase bound to Cu2+ specifically, and gene disruption mutagenesis of CopA resulted in an enhanced growth sensitivity of H. pylori to Cu2+ but not to other divalent cations. As determined experimentally, H. pylori CopA contains four pairs of transmembrane segments (H1 to H8), with the ATP binding and phosphorylation domains lying between H6 and H7, as found for another putative transition metal pump of H. pylori (K. Melchers, T. Weitzenegger, A. Buhmann, W. Steinhilber, G. Sachs, and K. P. Schäfer, J. Biol. Chem. 271:446-457, 1996). The corresponding transmembrane segments of the H. felis CopA pump were identified by hydrophobicity analysis and via sequence similarity. To define functional domains, similarly oriented regions of the two enzymes were examined for sequence identity. Regions with high degrees of identity included the N-terminal Cu2+ binding domain, the regions of ATP binding and phosphorylation in the energy transduction domain, and a transport domain consisting of the last six transmembrane segments with conserved cysteines in H4, H6, and H7. The data suggest that H. pylori and H. felis employ conserved mechanisms of ATPase-dependent copper resistance.

Adenosine Triphosphatases↗
PubMed1998

Properties and function of the P type ion pumps cloned from Helicobacter pylori.

Three distinct P type pumps were cloned from H. pylori 69A. Two of these pumps, ATPase 439 and ATPase 948 (CopA), were isolated by gene library screening using DNA oligonucleotide primers. Amino acid similarities found for the predicted proteins were about 50% to Cd2+/Cu2+ pumps. Gene disruption mutagenesis rendered the H. pylori knockout mutants more sensitive to Zn2+ and Cd2+ (ATPase 439) or Cu2+ (CopA). Some of the ATPase 439-deficient mutants were negative for urease activity while the majority of the mutants remained positive. Functional diversity of the pumps was also reflected by the ion affinities found for N-terminal peptides of CopA to Cu2+ and of ATPase 439 to Ni2+, Cu2+ and CO2+. The membrane domain of the two pumps were experimentally shown to consist of eight membrane spans. When ATPase 439 was expressed under control of a tac promoter in Escherichia coli, vanadate-sensitive phosphate accumulation was observed cytochemically along the membrane of the host cells. The third P type pump (ATPase 115) which also exhibited homology to transition metal ATPase was identified by sequencing a library of H. pylori membrane genes. The hydropathy plot of this pump was very similar to the former H. pylori ATPases whereas the N-terminal ion binding region was distinct. It was concluded that, in H. pylori, the presence of three transition metal ATPases with distinct ion specificity contributes to the adaptive mechanisms for gastric survival.

Adenosine Triphosphatases↗
PubMed1996

Cloning and membrane topology of a P type ATPase from Helicobacter pylori.

Southern blot screening of a genomic Helicobacter pylori library was employed to find a P type ATPase using a mixture of 16 DNA oligonucleotides coding for the DKTGT(I/L)T consensus sequence specific for the phosphorylation site of this family of ATPases. A positive clone, pRH439, was isolated and sequenced. The inserted 3.4-kb H. pylori DNA contained an intact open reading frame encoding a protein of 686 amino acids carrying the consensus sites for phosphorylation and ATP binding. The amino acid sequence exhibits a 25-30% identity with bacterial Cd2+ and Cu2+ ATPases. Genomic Southern blot analysis showed that this ATPase was present in all H. pylori strains examined, whereas it was not detectable in Campylobacter jejuni and other bacteria. The membrane topology of this ATPase was investigated using in vitro transcription/translation of fusion vectors to find signal anchor and/or stop transfer sequences. Eight regions of the H. pylori ATPase acted as signal anchor and/or stop transfer sequences and were ordered pairwise along the polypeptide chain placing the N and C-terminal amino acids in the cytoplasm. These transmembrane segments are contained between positions 73 and 92 (H1), 98 and 125 (H2), 128 and 148 (H3), 149 and 176 (H4), 309 and 327 (H5), 337 and 371 (H6), 637 and 658 (H7), and 659 and 685 (H8). The membrane domain of the ATPase, therefore, consists of at least four pairs of transmembrane segments with the phosphorylation site and ATP binding domain located in the large cytoplasmic loop between H6 and H7. The cytoplasmic domain contains several histidines and cysteines, perhaps indicative of divalent cation binding sites. There are several charged amino acids (3 Lys, 2 Glu, 2 Asp), predicted to be in the membrane domain mainly in H2, H3, and H4 and a Cys-Pro-Cys putative metal ion site in H6. The extracytoplasmic domain also has several charged amino acids (5 Glu, 1 Asp, 1 Lys, 1 Arg). It is likely that this novel protein is a heavy metal cation transporting ATPase and belongs to a family of P type ATPases containing eight transmembrane segments.

Adenosine Triphosphatases↗
PubMed1995

Structure and expression of the gene (HNRPA2B1) encoding the human hnRNP protein A2/B1.

Heterogeneous nuclear ribonucleoprotein (hnRNP) A2 is a major nuclear protein and one of the major components of the hnRNP core complex in mammalian cells. We first determined the complete sequence of the human gene for hnRNP protein A2 (HNRPA2B1). The human HNRPA2B1 gene exists in a single copy over 9 kb in length. The gene was split into 12 exons, including a 36-nucleotide mini-exon, which was specific to the hnRNP protein B1, providing genetic evidence that the B1 mRNA was generated from the primary HNRPA2B1 transcript by alternative splicing. The 5' region of HNRPA2B1 was GC-rich and contained several DNA motifs for the binding of several transcription factors, which included 2 CCAAT boxes and no TATA sequences. The 5' ends of the mRNA were mapped to multiple positions. These structural features are characteristic of promoter regions of housekeeping genes. Northern blot and RT-PCR analyses of the HNRPA2B1 transcripts revealed levels of B1 mRNA from 2 to 5% of total A2/B1 transcripts and showed that both A2 and B1 mRNAs were transcribed in all human cell lines and mouse tissues studied. The structural and evolutionary characteristics of the A2 and A1 proteins as they relate to each other are discussed.

Amino Acid Sequence↗
PubMed1995

Alveolar-to-vascular leakage of surfactant protein A in ventilated immature newborn rabbits.

We measured alveolar-to-vascular leakage of surfactant protein A (SP-A) in immature newborn rabbits delivered at a gestational age of 27 days. Experimental animals received, via a tracheal cannula, 2 ml/kg of a mixture of modified porcine surfactant (Curosurf, 80 mg/ml) and human recombinant SP-A (4 mg/ml). Littermate controls received the same volume of human SP-A in saline (4 mg/ml). After 30 min of artificial ventilation with a frequency of 40/min and an inspiration time of either 0.75 or 0.45 s, blood was sampled from the right ventricle and the lungs were lavaged. The content of human SP-A in serum and lung lavage fluid was determined with ELISA kits, and the alveolar-to-vascular leak expressed as the quotient of total SP-A in serum and lavage fluid. The leak in control animals amounted to about 2% of SP-A in lung wash and was several times higher in these animals than in those receiving surfactant. The leak was of the same order irrespective of whether the animals were ventilated with long or short inspiration time. We speculate that serum levels of SP-A may reflect the degree of lung injury in various forms of respiratory failure.

Animals↗
PubMed1992

Primary structure differences of human surfactant-associated proteins isolated from normal and proteinosis lung.

The primary structures of human pulmonary surfactant-associated proteins SP-A, SP-B and SP-C isolated from lung lavage of patients with alveolar proteinosis exhibit significant differences from lung surfactant proteins isolated from lungs of healthy individuals. In contrast to SP-A from normal lungs, proteinosis SP-A was shown by SDS gel electrophoresis to contain large amounts of unreducibly cross-linked beta chains. Specific primary structure modifications of SP-C and SP-B proteins were established by direct molecular weight and structural analysis, using [252Cf]plasma desorption mass spectrometry (PD/MS) as the principal method. In comparison to normal lung surfactant SP-B, proteinosis SP-B showed a significantly increased molecular weight by approx. 500 Da for the unreduced protein dimer. SP-C proteins from normal lungs were identified to possess a bis-cysteinyl-5,6-(thioester)palmitoylated structure, and to contain a frayed N-terminus resulting in two sequences of 34 and 35 amino acid residues. In contrast, SP-C from proteinosis patients was modified by (i) partial or even complete removal of palmitate residues and (ii) additional N-terminal proteolytic degradation. These results indicate the presence of pathophysiological structure modifications, which are likely to occur in the alveolar space, and may lead to a reduced surfactant function.

Amino Acid Sequence↗
PubMed1992

The C-terminal domain of the pulmonary surfactant protein C precursor contains signals for intracellular targeting.

We have studied the intracellular transport of the pulmonary surfactant SP-C precursor in vitro and in vivo. In order to monitor the route of the SP-C precursor, we constructed various C-terminally truncated forms of SP-C, which were tagged with a sequence derived from the C-terminus of the human c-myc gene (aa 409-419). Expression of these constructs under the control of the SV40 enhancer and the huMT-II promoter in stably transformed Chinese hamster ovary (CHO) cells revealed that the complete precursor molecule is localized mostly in vesicular structures, probably of lysosomal origin. The truncated precursor lacking the last 22 amino acids at the C-terminus (SP-C/Ctag), however, was restricted to the endoplasmic reticulum as shown by immunofluorescence, using antibodies directed against the tag-sequence, the lysosomal enzyme cathepsin D, the enzyme disulfide isomerase, and the Golgi zone. The intracellular localization was substantiated by subcellular fractionation analysis, suggesting that the last 22 amino acids are necessary for intracellular targeting. Furthermore, Triton X-114 extractions from CHO cells revealed a modification of the SP-C precursor. In vitro translation and pulse-chase experiments in the absence or presence of microsomes showed that the modification occurs post-translationally and in a time-dependent manner. Membrane association studies using an SP-C precursor lacking the mature peptide indicated that the modification is of hydrophobic nature but not a thioester-linked fatty acid.

Amino Acid Sequence↗
PubMed1991

The pulmonary surfactant protein C (SP-C) precursor is a type II transmembrane protein.

Human pulmonary-surfactant-associated protein C (SP-C) is an extremely hydrophobic peptide comprising 34-35 amino acids. It is involved in the reduction of surface tension at the air/liquid in the lung. In order to understand the mechanism by which this molecule is generated from its 197-amino-acid-residues-long precursor and secreted into the alveolar space, we analysed the biosynthesis and processing of this precursor in an 'in vitro' system. Our results show that the SP-C precursor is a 21 kDa integral membrane protein. It is anchored in the membrane by a hydrophobic domain that comprises the 20-amino-acid-residues-long hydrophobic core of the mature SP-C peptide. The N-terminus remains in the cytoplasm, which leads to a type II transmembrane orientation of the precursor. Membrane integration occurs in a signal-peptidase-independent manner. The hydrophobic domain acts as both signal sequence and membrane-anchoring domain. We suggest that correct membrane insertion of the SP-C precursor, which is strictly dependent on the hydrophobic-amino-acid sequence represented by the hydrophobic core of the mature SP-C, is itself a prerequisite for further processing and intracellular transport of the mature SP-C.

Animals↗
PubMed1991

Assembly of the surfactant protein SP-A. Deletions in the globular domain interfere with the correct folding of the molecule.

The C-terminal non-collagenous domain of the surfactant glycoprotein SP-A was shown to be essential for its correct folding and assembly, as judged by the secretion of various deletion mutants transiently expressed in COS cells. A deletion mutant coding for this domain was successfully secreted while the expression of the collagenous domain only did not lead to any detectable secretion. Deletion mutants lacking small parts of the non-collagenous domain interfered more or less with the correct folding and assembly of the molecule, thus either reducing or inhibiting the secretion. These data suggest that three prefolded non-collagenous domains register and act as a nucleation center for the folding of the collagenous triple helix which proceeds in a zipper-like fashion towards the N-terminus.

Base Sequence↗
PubMed1991

Structural comparison of recombinant pulmonary surfactant protein SP-A derived from two human coding sequences: implications for the chain composition of natural human SP-A.

The pulmonary surfactant-associated protein SP-A is encoded by presumably two different genes, resulting in slightly different amino acid sequences. Both gene products were expressed in Chinese hamster ovary cells. Their macromolecular structure differed significantly. SP-A alpha 3 exhibited a much higher amount of tetrameric to hexameric structures than SP-A alpha 2, for which dimeric structures predominate. These differences may be caused by the higher expression rates of SP-A alpha 3 presumably due to the presence of introns in the sequence. The occurrence of irregular disulfide links between individual oligomeric SP-A molecules composed of alpha 3-chains together with the demonstrated presence of both gene products in natural human SP-A suggest that the subunits of SP-A are heterotrimers of one alpha 2- and two alpha 3-chains.

Amino Acid Sequence↗
PubMed1990

Lung surfactant: a biotechnological challenge.

The genes for all three of the bona fide surfactant associated proteins have been cloned, allowing their production by recombinant DNA technology. In addition, improved protocols for the isolation of the natural surfactant proteins (NSP) made them available in larger quantities. Whereas, the NSP are often mixtures of allelic variants or functional isomers from gene families, the recombinant proteins (RSP) are obtained as single pure protein species. Antibodies directed against the N/RSP in combination with DNA probes have allowed new approaches to analyze the formation, location, transport, structure and functional capacities of these molecules as well as their interactions with one another and the phospholipids.

Amino Acid Sequence↗