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Biomedical subjects

A van Heerden

Publications and source records attributed to A van Heerden.

9 recordsLinked to original sources
PubMed2001

Temporary remission of disseminated paecilomycosis in a German shepherd dog treated with ketoconazole.

Disseminated mycosis caused by Paecilomyces varioti in a female German shepherd dog presented with chronic forelimb lameness is described. Radiographs of the swollen carpal joint revealed geographic lysis of the radial epiphysis. Diagnosis was based on cytological demonstration of fungal hyphae and chlamydiospores, as well as fungal culture of fluid obtained by arthrocentesis. Temporary remission was characterised by markedly improved clinical signs and laboratory parameters, following treatment with ketoconazole. The dog was euthanased 9 months after the initial diagnosis, following the diagnosis of multifocal discospondylitis. This appears to be the longest described period of temporary remission obtained with treatment in dogs with paecilomycosis. Clinical, clinicopathological and necropsy findings of this disease in another German shepherd dog are briefly described.

Animals↗
PubMed2000

Dirofilaria repens in a cat with acute liver failure.

Acute liver failure was diagnosed in a 12-year-old cat. Fine needle aspirate cytology revealed high numbers of unsheathed microfilariae and a hepatocellular reaction with no evidence of bacterial infection. The microfilariae were identified as those of Dirofilaria repens by acid phosphatase staining. The high number of microfilariae seen in both the blood and the liver aspirate samples as well as the favourable response to ivermectin amongst other drugs administered, is suggestive that D. repens was the cause of the liver insult. A positive result obtained with an antigen-capture ELISA (Dirochek) for Dirofilaria immitis antigen was interpreted as false. This is the 1st report of Dirofilaria repens for South Africa.

Acid Phosphatase↗
PubMed1998

Malignant fibrous histiocytoma of the deep peri-articular tissue of the stifle in a dog.

A Belgian shepherd dog aged 4 years and 9 months was presented with acute onset of non-weight bearing lameness and stifle effusion of the left hind limb, caused by the deep form of a malignant fibrous histiocytoma originating in the deep musculature and fascia surrounding the stifle joint. The tumour progressed rapidly in the tissues along the femoral diaphysis with marked periosteal new bone formation. Cytology of a stifle joint aspirate revealed numerous large polygonal neoplastic cells with considerable anisocytosis and anisokaryosis. These cells were present in clusters, with cytoplasmic projections between the cells, but occasionally also occurred singly. Several cells contained multiple cytoplasmic vacuoles and occasional giant cells were also encountered. Adequate tumour-free margins were not possible with radical limb amputation and the dog was euthanased. Macroscopically the tumour appeared as an extensive pale tan, firm mass with scattered small haemorrhages and foci of yellow discolouration. Histologically the tumour consisted of dense neoplastic expanses or multiple nodules, composed of spindle-shaped fibroblastic cells, polygonal histiocytic cells or cell clusters and scattered giant cells with 2-3 nuclei. The polygonal neoplastic cells were frequently present around and invading lymphatics and blood vessels, causing neoplastic emboli. This is the 1st report of the clinical behaviour, radiography and cytology of the deep form of malignant fibrous histiocytoma in the dog.

Animals↗
PubMed1996

pH-dependent and ligand induced conformational changes of eucaryotic protein synthesis initiation factor eIF-(iso)4F: a circular dichroism study.

The structural features of wheat germ protein synthesis initiation factor eIF-(iso)4F, which has a cap binding protein as one of its two subunits, are unknown. In this study, circular dichroism (CD) spectra and secondary structure prediction were obtained for eIF-(iso)4F and its two subunits, p28 and p86. The alpha-helix content of eIF-(iso)4F changed from 42% at pH 6.3 to 15% at pH 7.6, the optimum pH for cap binding. The beta-sheet content increased from 14% (pH 6.3) to 38% at pH 7.6. The CD spectra of the two subunits, p28 and p86 were also measured and analyzed. The separated subunits both had a higher alpha-helix content at pH 7.6 than the native protein, giving values of 60% and 34% alpha-helix for p28 and p86, respectively. Binding of the dinucleotide cap analog to p28 reduced the alpha-helix content to approximately 8% with an increase in the beta sheet content from 10% to 37%. The conformational changes in eIF-(iso)4F upon binding with mRNA are dependent on cap or oligonucleotide structure. A conformation consisting of approximately the same alpha-helix and beta-sheet content can be induced by ligands even at non-optimal pH values. This large conformational transition suggests eIF-(iso)4F binds nucleic acids by interaction of a beta-sheet motif and that this conformational transition may have a regulatory role.

Circular Dichroism↗
PubMed1996

Human skeletal muscle nebulin sequence encodes a blueprint for thin filament architecture. Sequence motifs and affinity profiles of tandem repeats and terminal SH3.

Analysis of deduced protein sequence and structural motifs of approximately 5500 residues of human fetal skeletal muscle nebulin reveals the design principles of this giant multifunctional protein in the sarcomere. The bulk of the sequence is constructed of approximately 150 tandem copies of approximately 35-residue modules that can be classified into seven types. The majority of these modules form 20 super-repeats, with each super-repeat containing a 7-module set (one of each type in the same order). These super-repeats are further divided into eight segments: with six segments containing adjacent, highly homologous super-repeats, one single repeat segment consisting of 8 nebulin modules of the same type, and a non-repeat segment terminating with a SH3 domain at the C terminus. The interactions of actin, tropomyosin, troponin, and calmodulin with nebulin fragments consisting of either repeating modules or the SH3 domain support its role as a giant actin-binding cofilament of the composite thin filament. Such affinity profiles also suggest that nebulin may bind to tropomyosin and troponin to form a composite calcium-linked regulatory complex on the thin filament. The modular construction, super-repeat structure, and segmental organization of nebulin sequence appear to encode thin filament length, periodicity, insertion, and sarcomere proportion in the resting muscle.

Actin Cytoskeleton↗
PubMed1995

Interaction of wheat germ protein synthesis initiation factor eIF-(iso)4F and its subunits p28 and p86 with m7GTP and mRNA analogues.

The binding of p28, p86, and native wheat germ eIF-(iso)4F with m7GTP and oligonucleotides was measured and compared. The purified subunits (p28, 28 kDa and p86, 86 kDa) of wheat germ protein synthesis initiation factor eIF-(iso)4F have been obtained from Escherichia coli expression of the cloned DNA (van Heerden, A., and Browning, K. S. (1994) J. Biol. Chem. 269, 17454-17457). The binding of the 5'-terminal cap analogue m7GTP to the small subunit (p28) of eIF-(iso)4F as a function of pH, temperature, and ionic strength is described. The mode of binding of p28 to cap analogues is very similar to the intact protein. Assuming that all tryptophan residues contribute to p28 and eIF-(iso)4F fluorescence, iodide quenching shows that all 9 tryptophan residues in p28 are solvent-accessible, while only 6 out of 16 tryptophan residues are solvent-accessible on the intact eIF-(iso)4F. The fluorescence stopped-flow studies of eIF-(iso)4F and p28 with cap show a concentration-independent conformational change. The rate of this conformational change was approximately 10-fold faster for the isolated p28 compared with the native eIF-(iso)4F. From these studies it appears that cap recognition resides in the p28 subunit. However, p86 enhances the interaction with capped oligonucleotides and probably is involved in protein-protein interactions as well. Both subunits are required for helicase activity.

Base Sequence↗
PubMed1995

Function of the p86 subunit of eukaryotic initiation factor (iso)4F as a microtubule-associated protein in plant cells.

The isozyme form of eukaryotic initiation factor 4F [eIF-(iso)4F] from wheat germ is composed of a p28 subunit that binds the 7-methylguanine cap of mRNA and a p86 subunit having unknown function. The p86 subunit was found to have limited sequence similarity to a kinesin-like protein encoded by the katA gene of Arabidopsis thaliana. Native wheat germ eIF-(iso)4F and bacterially expressed p86 subunit and p86-p28 complex bound to taxol-stabilized maize microtubules (MTs) in vitro. Binding saturation occurred at 1 mol of p86 per 5-6 mol of polymerized tubulin dimer, demonstrating a substoichiometric interaction of p86 with MTs. No evidence was found for a direct interaction of the p28 subunit with MTs. Unlike kinesin, cosedimentation of eIF-(iso)4F with MTs was neither reduced by MgATP nor enhanced by adenosine 5'-[gamma-imido]triphosphate. Both p86 subunit and p86-p28 complex induced the bundling of MTs in vitro. The p86 subunit was immunolocalized to the cytosol in root maize cells and existed in three forms: fine particles, coarse particles, and linear patches. Many coarse particles and linear patches were colocalized or closely associated with cortical MT bundles in interphase cells. The results indicate that the p86 subunit of eIF-(iso)4F is a MT-associated protein that may simultaneously link the translational machinery to the cytoskeleton and regulate MT disposition in plant cells.

Arabidopsis Proteins↗
PubMed1994

Expression in Escherichia coli of the two subunits of the isozyme form of wheat germ protein synthesis initiation factor 4F. Purification of the subunits and formation of an enzymatically active complex.

The subunits (p28 and p86) of the isoenzyme form of eukaryotic initiation factor 4F (eIF-(iso)4F) from wheat were expressed separately in Escherichia coli. The subunits were purified by affinity chromatography (p28) and ion-exchange chromatography (p86). The purified subunits alone did not support polypeptide synthesis in an eIF-(iso)4F and eIF-4F-deficient translation system from wheat germ. However, when the two subunits were mixed together, activity equal to that of the native form of eIF-(iso)4F was obtained. These results show that subunits expressed separately are able to associate and form an enzymatically active complex.

Base Sequence↗