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W P Clark

Publications and source records attributed to W P Clark.

9 recordsLinked to original sources
PubMed1997

Killer cell inhibitory receptors: diversity, specificity, and function.

NK cells selectively kill target cells that fail to express self-MHC class I molecules. This selective killing results from a balance between inhibitory NK receptors specific for MHC class I molecules and activating receptors that are still largely unknown. Isolation of molecular clones for the human killer cell inhibitory receptors (KIR) revealed that KIR consist of a family of molecules with Ig ectodomains and cytoplasmic tails of varying length. Soluble complexes of KIR and HLA-C molecules established that KIR recognizes and binds to its ligand as an autonomous receptor. A functional expression system in human NK clones demonstrated that a single KIR can provide both recognition of MHC class I and delivery of a dominant negative signal to the NK cell. Functional evidence has been obtained for a role of the tyrosine phosphatase SHP-1 in KIR-mediated inhibition. The presence of a conserved motif used to recruit and activate SHP-1 in the cytoplasmic tail of KIR and of the mouse Ly-49 inhibitory receptor (otherwise structurally unrelated to KIR) represents an interesting case of evolutionary convergence. Furthermore, the motif led to the identification of other receptors with inhibitory potential, including a type I Ig-like receptor shared by mouse mast cells and NK cells.

Amino Acid Sequence↗
PubMed1993

ClpX, an alternative subunit for the ATP-dependent Clp protease of Escherichia coli. Sequence and in vivo activities.

The ATP-dependent Clp protease of Escherichia coli consists of two subunits, the ClpP subunit, which has the proteolytic active site, and ClpA, which possesses ATPase activity and activates the proteolytic activity of ClpP in vitro. Recently, Zylicz and co-workers (Wojtkowiak, D., Georgopoulos, C., and Zylicz, M. (1993) J. Biol. Chem. 268, 22609-22617) identified another E. coli protein that activated ATP-dependent degradation of lambda O protein in the presence of ClpP. The amino-terminal sequence of this protein corresponds to the translated amino-terminal sequence of a gene that we have named clpX. clpX encodes a protein with M(r) 46,300, similar to that observed for the protein purified by Wojtkowiak et al. clpX is an operon with clpP; both genes are cotranscribed in a single heat-inducible 2200-base mRNA, with clpP the promoter proximal gene. The sequence of ClpX includes a single consensus ATP-binding site motif and has limited homology to regions of ClpA and other members of the ClpA/B/C family. A third group of proteins, ClpY, closely related to ClpX, has been identified by sequence homology. Mutations in either clpX or clpP abolish degradation of the highly unstable lambda O protein in vivo. clpX mutants are not defective in degradation of previously identified ClpA/ClpP substrates such as a ClpA-beta-galactosidase fusion protein. It appears that selectivity of degradation by ClpP in vivo is determined by interaction of ClpP with different regulatory ATPase subunits.

ATP-Dependent Proteases↗
PubMed1990

Sequence and structure of Clp P, the proteolytic component of the ATP-dependent Clp protease of Escherichia coli.

The ATP-dependent Clp protease of Escherichia coli contains two dissimilar components: the Clp A regulatory polypeptide, with two ATP binding sites and intrinsic ATPase activity, and the Clp P subunit, which contains the proteolytic active site. The DNA sequence of the clpP gene predicts a protein of 207 amino acids (Mr 21,679), which is in close agreement with the size determined by sodium dodecyl sulfate-gel electrophoresis of purified Clp P. Clp P has a native Mr of approximately 240,000, and electron micrographs of the protein show superimposed disk-like structures with a central cavity, similar in appearance to purified proteasomes from eukaryotic cells. Clp P is synthesized with a 14-amino acid leader which is rapidly cleaved in vivo to yield the 193-amino acid protein which has activity in vitro. The clpP gene is at 10 min on the E. coli map, close to that for the ATP-dependent Lon protease of E. coli and far from the gene for clpA. Primer extension experiments indicate that transcription initiates immediately upstream of the coding region for Clp P, with a major transcription start at 120 bases in front of the start of translation. Insertion mutations in clpP have been isolated and transferred to the chromosome; strains devoid of Clp P are viable in the presence or absence of Lon protease. Mutations in clpP stabilize the same Clp A-beta-galactosidase fusion protein specifically stabilized by clpA mutations, providing the first genetic evidence that Clp A and Clp P act together in vivo.

ATP-Dependent Proteases↗
PubMed1990

Clp P represents a unique family of serine proteases.

The amino acid sequence of Clp P, the proteolytic subunit of the ATP-dependent Clp protease of Escherichia coli, closely resembles a protein encoded by chloroplast DNA, which is well conserved between chloroplasts of different plant species. The homology extends over almost the full length of the sequences of both proteins and consists of approximately 46% identical and approximately 70% similar amino acids. Antibodies against E. coli Clp P cross-reacted with proteins with Mr of 20,000-30,000 in bacteria, lower eukaryotes, plants, and animal cells. Since the regulatory subunit of Clp protease, Clp A, also has a homolog in plants, as well as in other bacteria and in lower eukaryotes, it is likely that ATP-dependent proteolysis in chloroplasts is catalyzed in part by a Clp-like protease and that both components of Clp-like proteases are widespread in living cells. We have identified Ser-111 as the active site serine in E. coli Clp P modified by diisopropyl fluorophosphate. Mutational alteration of Ser-111 or His-136 eliminates proteolytic activity of Clp P. Both residues are found in highly conserved regions of the protein. The sequences around the active site residues suggest that Clp P represents a unique class of serine protease. Amino-terminal processing of cloned Clp P mutated at either Ser-111 or His-136 occurs efficiently when wild-type clpP is present in the chromosome but is blocked in clpP- hosts. Processing of Clp P appears, therefore, to involve an intermolecular autocatalytic cleavage reaction. Since processing of Clp P occurs in clpA- cells, the autoprocessing activity of Clp P is independent of Clp A.

ATP-Dependent Proteases↗
PubMed1990

The ATP-dependent Clp protease of Escherichia coli. Sequence of clpA and identification of a Clp-specific substrate.

The clpA gene, which codes for the ATP-binding subunit of the ATP-dependent Clp protease of Escherichia coli, has been sequenced. The coding region contains a single open reading frame for a protein of 758 amino acids; within the amino acid sequence are two consensus sequences for ATP-binding sites. The sequence of ClpA does not resemble that of other previously described ATPases or Lon, the other sequenced ATP-dependent protease of E. coli, except in the ATP-binding site consensus region. The clpA gene is expressed as a monocistronic message. Primer extension experiments define a major start point of transcription at -183 relative to the start of translation. A rho-independent terminator is located 23 bases beyond the end of the coding region. The ClpA protein is degraded in vivo in a Clp-dependent fashion (t1/2 approximately 60 min). A fusion protein containing the first 40 amino acids of ClpA fused in frame to beta-galactosidase is degraded very rapidly in a clpA+ host (t1/2 approximately 3 min) but not in a clpA- host. This fusion protein is the first Clp-specific substrate described.

ATP-Dependent Proteases↗
PubMed1989

Organization and sequence of the genes coding for the proton-translocating ATPase of Bacillus megaterium.

We have cloned and sequenced the genes for the subunits of the proton-translocating ATP synthase of Bacillus megaterium QM B1551. The arrangement of the genes is identical to the arrangement of the same genes (the unc operon) in Escherichia coli. The genes for the Fo subunits immediately precede the genes for the F1 subunits and are themselves preceded by an open reading frame which codes for a protein similar to the E. coli i protein. In contrast to the E. coli ATPase genes, the transcript for these ATPase genes does not include this open reading frame.

Amino Acid Sequence↗
PubMed1988

The two-component, ATP-dependent Clp protease of Escherichia coli. Purification, cloning, and mutational analysis of the ATP-binding component.

The ATP-binding component (Component II, hereafter referred to as ClpA) of a two-component, ATP-dependent protease from Escherichia coli has been purified to homogeneity. ClpA is a protein with subunit Mr 81,000. It has an intrinsic ATPase activity and activates degradation of protein substrates only in the presence of a second component (Component I, hereafter referred to as ClpP), Mg2+, and ATP. The amount of ClpA varies by less than a factor of 2 in cells grown in different media and at temperatures from 30 to 42 degrees C. ClpA does not appear to be a heat-shock protein since its synthesis is not dependent on htpR. Antibodies against purified ClpA were used to identify lambda transducing phage bearing the clpA gene. The cloned gene contains a DNA sequence expected to code for the first 28 amino acids of ClpA, which were determined by protein sequencing of purified ClpA. The clpA gene in the phage was mutated by insertion of delta kan defective transposons and the mutations were transferred to E. coli by homologous recombination. The clpA gene was mapped to 19 min on the E. coli chromosome. Mutant cells with insertions early in the gene produce no ClpA protein detectable in Western blots, and extracts of such mutant cells have no detectable ClpA activity. clpA- mutants grow well under all conditions tested and are not defective in turnover of proteins during nitrogen starvation nor in the turnover of such highly unstable proteins as the lambda proteins O, N, and cII, or the E. coli proteins SulA, RcsA, and glutamate dehydrogenase. The degradation of abnormal canavanine-containing proteins is defective in clpA mutants especially in cells that also have a lon- mutation. Extracts of clpA- lon- cells have ATP-dependent casein degrading activity.

ATP-Dependent Proteases↗
PubMed1981

Diaphragmatic disruption secondary to blunt abdominal trauma.

A 3-year experience with diaphragmatic disruption secondary to blunt trauma was reviewed. Seventy-five per cent of the disruptions were on the left side and the incidence of associated intra-abdominal and thoracic injuries was 100%. Disruption occurred in two distinct anatomic positions: 1) through the central tendon; 2) at the lateral costal insertion. Diagnosis was usually made by plain X-ray films of the chest, occasionally with the aid of fluoroscopy. Difficulty was encountered making the diagnosis preoperatively, especially when there was significant hemothorax and/or pulmonary contusion. Angiography was diagnostic in three cases. Careful examination of the diaphragm in all blunt abdominal cases is essential to avoid delay in diagnosis. In the patients with an associated ruptured hollow viscus there was high incidence of empyema leading to severe morbidity. In such cases concomitant thoracotomy at the time of definitive therapy should be considered. The mortality of this injury is primarily related to the incidence of associated injuries and pre-existing, nontraumatic disease. Diaphragmatic disruption rarely occurs alone in blunt trauma. Laparotomy is required for control of hemorrhage in most cases.

Abdominal Injuries↗