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Biomedical subjects

A C Wallace

Publications and source records attributed to A C Wallace.

At least 19 recordsLinked to original sources
PubMed1998

Prion protein selectively binds copper(II) ions.

The infectious isoform of the prion protein (PrPSc) is derived from cellular PrP (PrPC) in a conversion reaction involving a dramatic reorganization of secondary and tertiary structure. While our understanding of the pathogenic role of PrPSc has grown, the normal physiologic function of PrPC still remains unclear. Using recombinant Syrian hamster prion protein [SHaPrP(29-231)], we investigated metal ions as possible ligands of PrP. Near-UV circular dichroism spectroscopy (CD) indicates that the conformation of SHaPrP(29-231) resembles PrPC purified from hamster brain. Here we demonstrate by CD and tryptophan (Trp) fluorescence spectroscopy that copper induces changes to the tertiary structure of SHaPrP(29-231). Binding of copper quenches the Trp fluorescence emission significantly, shifts the emission spectrum to shorter wavelengths, and also induces changes in the near-UV CD spectrum of SHaPrP(29-231). The binding sites are highly specific for Cu2+, as indicated by the lack of a change in Trp fluorescence emission with Ca2+, Co2+, Mg2+, Mn2+, Ni2+, and Zn2+. Binding of Cu2+ also promotes the conformational shift from a predominantly alpha-helical to a beta-sheet structure. Equilibrium dialysis experiments indicate a binding stoichiometry of approximately 2 copper molecules per PrP molecule at physiologically relevant concentrations, and pH titration of Cu2+ binding suggests a role for histidine as a chelating ligand. NMR spectroscopy has recently demonstrated that the octarepeats (PHGGGWGQ) in SHaPrP(29-231) lack secondary or tertiary structure in the absence of Cu2+. Our results suggest that each Cu2+ binds to a structure defined by two octarepeats (PHGGGWGQ) with one histidine and perhaps one glycine carbonyl chelating the ion. We propose that the binding of two copper ions to four octarepeats induces a more defined structure to this region.

Animals↗
PubMed1997

Evidence for protein X binding to a discontinuous epitope on the cellular prion protein during scrapie prion propagation.

Studies on the transmission of human (Hu) prions to transgenic (Tg) mice suggested that another molecule provisionally designated protein X participates in the formation of nascent scrapie isoform of prion protein (PrPSc). We report the identification of the site at which protein X binds to the cellular isoform of PrP (PrPC) using scrapie-infected mouse (Mo) neuroblastoma cells transfected with chimeric Hu/MoPrP genes even though protein X has not yet been isolated. Substitution of a Hu residue at position 214 or 218 prevented PrPSc formation. The side chains of these residues protrude from the same surface of the C-terminal alpha-helix and form a discontinuous epitope with residues 167 and 171 in an adjacent loop. Substitution of a basic residue at positions 167, 171, or 218 also prevented PrPSc formation: at a mechanistic level, these mutant PrPs appear to act as "dominant negatives" by binding protein X and rendering it unavailable for prion propagation. Our findings seem to explain the protective effects of basic polymorphic residues in PrP of humans and sheep and suggest therapeutic and prophylactic approaches to prion diseases.

Animals↗
PubMed1997

TESS: a geometric hashing algorithm for deriving 3D coordinate templates for searching structural databases. Application to enzyme active sites.

It is well established that sequence templates such as those in the PROSITE and PRINTS databases are powerful tools for predicting the biological function and tertiary structure for newly derived protein sequences. The number of X-ray and NMR protein structures is increasing rapidly and it is apparent that a 3D equivalent of the sequence templates is needed. Here, we describe an algorithm called TESS that automatically derives 3D templates from structures deposited in the Brookhaven Protein Data Bank. While a new sequence can be searched for sequence patterns, a new structure can be scanned against these 3D templates to identify functional sites. As examples, 3D templates are derived for enzymes with an O-His-O "catalytic triad" and for the ribonucleases and lysozymes. When these 3D templates are applied to a large data set of nonidentical proteins, several interesting hits are located. This suggests that the development of a 3D template database may help to identify the function of new protein structures, if unknown, as well as to design proteins with specific functions.

Algorithms↗
PubMed1996

Derivation of 3D coordinate templates for searching structural databases: application to Ser-His-Asp catalytic triads in the serine proteinases and lipases.

It is well established that sequence templates (e.g., PROSITE) and databases are powerful tools for identifying biological function and tertiary structure for an unknown protein sequence. Here we describe a method for automatically deriving 3D templates from the protein structures deposited in the Brookhaven Protein Data Bank. As an example, we describe a template derived for the Ser-His-Asp catalytic triad found in the serine proteases and triacylglycerol lipases. We find that the resultant template provides a highly selective tool for automatically differentiating between catalytic and noncatalytic Ser-His-Asp associations. When applied to nonproteolytic proteins, the template picks out two "non-esterase" catalytic triads that may be of biological relevance. This suggests that the development of databases of 3D templates, such as those that currently exist for protein sequence templates, will help identify the functions of new protein structures as they are determined and pinpoint their functionally important regions.

Amino Acid Isomerases↗
PubMed1995

LIGPLOT: a program to generate schematic diagrams of protein-ligand interactions.

The LIGPLOT program automatically generates schematic 2-D representations of protein-ligand complexes from standard Protein Data Bank file input. The output is a colour, or black-and-white, PostScript file giving a simple and informative representation of the intermolecular interactions and their strengths, including hydrogen bonds, hydrophobic interactions and atom accessibilities. The program is completely general for any ligand and can also be used to show other types of interaction in proteins and nucleic acids. It was designed to facilitate the rapid inspection of many enzyme complexes, but has found many other applications.

Algorithms↗
PubMed1995

Establishing a district palliative care team for children.

The children's palliative care team aims to ensure a high standard of care and support for children with life-threatening illnesses and their families. The team works through primary care teams and with hospital staff to ensure consistency and continuity of care and to maintain awareness of good practice and acts as a resource for staff from independent and voluntary agencies. The team consists of a consultant community paediatrician, clinical child psychologist, a dedicated social worker, sick children's trained district nurse, a senior member of staff from the children's ward, a health visitor, a school nurse, and a special school nurse. Other professionals are co-opted to the team as and when considered necessary, for example hospice consultant, pain specialist, dietician, paediatric pharmacist, chaplain. This paper describes how the children's palliative care team was set up and the first 2 years of its functioning.

Child↗
PubMed1992

Distribution of Lipiodol and evidence for tumor necrosis in hepatocellular carcinoma.

To study the distribution and thromboembolic effect of Ultrafluid Lipiodol, 15 surgically removed hepatocellular carcinomas with selective intraarterial Lipiodol injection 7 to 10 days before surgery and 15 noninjected controls were studied radiologically and histologically. Tissue blocks were processed with an en bloc silver impregnation technique for Lipiodol localization in histologic sections. Lipiodol was distributed evenly in tumors measuring less than 5 cm in diameter and peripherally in tumors measuring 10 cm or more. Lipiodol droplets were mainly extracellular. There was no difference in tumor architecture or in hemorrhage and necrosis scores between Lipiodol-injected cases and negative controls (1.18 versus 0.92). Similarly, in injected cases, no differences were observed between Lipiodol-positive and Lipiodol-negative areas (scores of x-ray Lipiodol-positive versus Lipiodol-negative areas: 1.17 versus 1.36; scores of microscopic Lipiodol-positive versus Lipiodol-negative areas: 1.18 versus 1.14). Lipiodol-negative but hypodense areas examined by x-ray proved to be necrosis or fibrosis with or without viable tumor islands. Lipiodol has no thromboembolic effects. The uneven Lipiodol distribution may account for its failure as a carrier for chemotherapeutic agents in large tumors.

Carcinoma, Hepatocellular↗
PubMed1991

Kidney biopsy findings in cyclosporine-treated patients with insulin-dependent diabetes mellitus.

Renal biopsy specimens of 40 patients with recent-onset insulin-dependent diabetes mellitus treated with cyclosporine (CSA) for 6-29 months were examined. Cyclosporine-associated chronic vascular interstitial toxicity of moderate intensity was found in 10 patients (25%). The most prominent lesions were interstitial fibrosis and tubular atrophy. Arteriolopathy was less pronounced and glomerular damage unremarkable. A significant correlation exists between the extent of tubular atrophy and CSA trough whole blood levels. These data indicate that the development of CSA-associated chronic nephropathy is dose-dependent.

Adolescent↗
PubMed1990

Demonstration of Lipiodol in paraffin sections using a modified silver impregnation technique.

To demonstrate postangiographic Lipiodol (LIP) in hepatocellular carcinoma (HCC) in paraffin sections, direct impregnation of formalin-fixed tissue blocks with silver nitrate (AgNO3) was followed by routine processing. LIP appeared as black globules in the sinusoids. Ninety-four tissue blocks from 13 postangiographic LIP HCCs and 69 from 8 non-LIP HCCs and 4 fatty livers were studied. Seventy-two of 73 negative controls and all positive blocks as seen on soft tissue radiographs (STRs) were correctly coded (specificity 98.6%, sensitivity 100%). Twenty-six of the 44 LIP-negative areas on STRs from LIP cases contained scanty globules of less than 10 microns in diameter. Fatty change gave no positive readings. Thus, modified AgNO3 impregnation is a simple, accurate means of detecting LIP in high-quality paraffin sections suitable for tumor diagnosis and, if applied to postangiographic LIP, ultrasonographically guided liver biopsy, can verify that a biopsy has reached a suspected tumor focus.

Biopsy↗
PubMed1989

Primary acute renal failure ("acute tubular necrosis") in the transplanted kidney: morphology and pathogenesis.

"Acute tubular necrosis" (ATN) in the transplanted kidney, when properly differentiated from other causes of acute renal failure, appears to be a relatively benign condition. It has been widely assumed to be pathologically identical to ATN in the native kidney, but its histopathologic features have not been studied in detail. Because immunosuppressive therapy with cyclosporine adds an additional layer of complexity to the morphologic changes observed, in the present study we have confined our observations to patients immunosuppressed with steroids and azathioprine. Thirteen renal allograft biopsies from patients with ATN and 5 biopsies from patients with normal allograft function were compared with the previously obtained series of 57 native kidney ATN biopsies and 20 control biopsies. Both qualitative and quantitative differences between transplant and native kidney ATN were found. Compared with native kidney ATN, transplant ATN showed significantly less thinning and absence of proximal tubular brush border and less variation in size and shape of cells in individual tubular cross-sections. There were also significantly fewer casts and less dilatation of Bowman's space and a significantly greater number of polarizable crystals presumed to be oxalate in transplant ATN. In native kidney ATN the tubular injury sites were mostly characterized by desquamation of individual epithelial cells leaving areas of bare basement membrane (the "non-replacement" phenomenon). In transplant ATN, sites of tubular injury, although rare and affecting only short tubular segments, were characterized by the actual presence of identifiable necrotic tubular cells, a finding seldom seen in native kidney ATN. There also was a greater interstitial infiltrate of mononuclear inflammatory cells in transplant ATN compared to native kidney ATN. Electron microscopic studies of 9 transplant ATN biopsies showed a mild reduction in proximal tubular brush border compared with controls but this alteration was significantly less than that observed in native kidney ATN. There was no significant alteration in proximal or distal basolateral infoldings and this contrasted sharply with the marked reduction in basolateral infoldings of the plasma membrane observed in native kidney ATN. Disintegrated necrotic cells were found by electron microscopy in transplant ATN whereas these were not observed in native kidney ATN. There were significantly more cells with apoptosis (shrinkage necrosis) in transplant ATN than in native kidney ATN. There were significantly more cells with apoptosis (shrinkage necrosis) in transplant ATN than in native kidney ATN. On the other hand, there were significantly greater numbers of "non-replacement" sites in the distal tubules in native kidney ATN compared to transplant ATN.(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗
PubMed1988

IgA nephropathy in relapsing polychondritis.

Relapsing polychondritis (RP) is a multisystem autoimmune disease characterized by the presence of antibodies to type II collagen. This collagen is found predominantly in cartilaginous tissues, vitreous humor, aorta and notochord. Involvement of the kidney is rare, only 7 cases having been recorded, and there is no type II collagen in glomeruli. Six of the previous cases had crescentic glomerulonephritis. We report here two cases of biopsy proven RP in which IgA nephropathy was seen, the first examples recorded. Both patients had hematuria and slight proteinuria, with mild impairment of renal function. The histological and immunofluorescence pattern on both biopsies was in keeping with IgA nephropathy. Both patients received steroids with diminution/disappearance of hematuria and proteinuria. In view of the potentially progressive nature of glomerular disease with RP, the renal status should be investigated in all patients with RP.

Adult↗
PubMed1987

Effect of cyclosporine on the kidney.

Cyclosporine constitutes a major advance in pharmacologic immunosuppression, the benefit of which is now established for solid organ transplantation and is rapidly emerging for many forms of autoimmune disease. By virtue of its potency and selectivity, there has been a marked reduction in steroid requirement with a concomitant reduction in morbidity and mortality. The undesirable effect of cyclosporine on the kidney may thus be considered within this context. The short-term functional effect observed to some degree in most patients receiving this drug is rapidly reversible, and is unaccompanied by long-term detriment in studies now extending over 6 years. Progressive deterioration still occurs in a small proportion of patients, but may often be reversed by carefully controlled conversion to alternative combination immunosuppression therapy. For each developing application, the ultimate value of cyclosporine must be determined individually in relation to the severity of the disease process. The challenge that now confronts us is to determine the manner in which this agent may be most safely and effectively used.

Animals↗
PubMed1986

Dextran microsphere embolization: experimental and clinical experience with radiologic-pathologic correlation. Work in progress.

The radiologic and pathologic effects of canine renal embolization with dextran microspheres of two size ranges (40-150 micron and 100-300 micron) were studied 30 minutes and 1, 2, 4, and 6 weeks after embolization. Dramatic occlusions occurred with very small quantities of these particles, which reached more distally and were suspended and embolized more easily than other solid embolic agents. Because of these qualities, however, they should be used with more caution. They can be injected through 2-F catheters, calibrated-leak balloons, and open-ended guide wires. Embolization with dextran microspheres was also used for epistaxis, meningioma, dural arteriovenous malformation, renal tumors, bone metastasis, multiple myeloma, or peripheral angioma in ten patients. The technique was safe and effective, but special attention should be directed to proper dilution and gentle embolization with careful monitoring to avoid excessive embolization or reflux.

Animals↗
PubMed1985

Multicentric reticulohistiocytosis: a report of a case and a review of the pathology.

A case of multicentric reticulohistiocytosis (MR) in a 24-yr-old woman is presented. MR is a rare disorder characterized by progressive polyarthropathy and a papulo-nodular skin rash. The diagnosis was established by histological examination of biopsies of erythematous nodules on the fingers which showed circumscribed collections of large mononuclear cells and multinucleate giant cells in the reticular dermis. These were embedded in a fine network of mature fibrous tissue with a scanty lymphocytic infiltrate. Histochemical, immunopathological and ultrastructural investigations confirmed that the large mononuclear cells had the properties of macrophages. The histopathological features of MR are reviewed in the light of current knowledge of macrophage physiology, and evidence for lymphocyte-histiocyte interactions in the pathogenesis of this bizarre granulomatous disorder is presented.

Adult↗