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A J Rowe

Publications and source records attributed to A J Rowe.

At least 37 records · Page 2Linked to original sources
PubMed1994

Modeling the bacterial protein toxin, pneumolysin, in its monomeric and oligomeric form.

Pneumolysin is a member of the family of related bacterial thiol-activated toxins, which share structural similarities and a proposed common cytolytic mechanism. Currently the molecular mechanism of membrane damage caused by these toxins remains a matter of controversy. A prerequisite for defining this mechanism is a detailed knowledge of the monomeric and oligomeric pneumolysin structures. We present for the first time details of the monomeric structure of a thiol-activated toxin, pneumolysin. Electron microscope images of metal-shadowed pneumolysin monomers show an asymmetric molecule composed of four domains. We have studied the conformation of pneumolysin monomer by low resolution hydrodynamic bead modeling procedures. The bead model dimensions and shape are derived solely from the electron micrographs. The bead model has been evaluated in terms of the predicted solution properties, which in turn have been compared to the experimental values of the sedimentation coefficient, s(20,w)0, obtained by analytical ultracentrifugation and the intrinsic viscosity, [eta]. Pneumolysin oligomers, observed as ring- and arc-shaped structures, were also examined by electron microscopy. Metal shadowing and negative staining methods were used to establish the overall dimensions of the oligomer and were used to produce a morphological model for the oligomer, incorporating monomer subunits based on the hydrodynamic bead model.

Animals↗
PubMed1994

Identification of the vinculin-binding site in the cytoskeletal protein alpha-actinin.

Using low-speed sedimentation equilibrium we have established that vinculin binds to alpha-actinin with a Kd of 1.3 x 10(-5) M. Electron microscopy of negatively stained preparations of vinculin revealed spherical particles (diameter 11.2 nm; S.D. 1.7 nm, n = 21), whereas alpha-actinin appeared as a rod-shaped particle (length 33 nm; S.D. 3.3 nm, n = 23). Mixtures of the two proteins contained both 'lollipop'- and 'dumbell'-shaped particles which we interpret as either one or two spherical vinculin molecules associated with the ends of the alpha-actinin rod. We have further defined the vinculin-binding site in alpha-actinin using 125I-vinculin and a gel-blot assay in which proteolytic fragments of alpha-actinin and fragments of alpha-actinin expressed in Escherichia coli were resolved by SDS/PAGE and blotted to nitrocellulose. 125I-vinculin bound to polypeptides derived from the spectrin-like repeat region of alpha-actinin, but did not bind to the actin-binding domain. Binding was inhibited by a 100-fold molar excess of unlabelled vinculin. Using a series of glutathione S-transferase fusion proteins we have mapped the vinculin-binding site to a region toward the C-terminal end of the molecule (alpha-actinin residues 713-749). 125I-vinculin also bound to fusion proteins containing this sequence which had been immobilized on glutathione-agarose beads. The vinculin-binding site is localized in a highly conserved region of the molecule close to the first of two EF-hand calcium-binding motifs.

Actinin↗
PubMed1994

Product-induced stabilization of tertiary and quaternary structure in Escherichia coli dehydroquinase.

The effects of irreversibly attaching product at the active site of type I dehydroquinase from Escherichia coli have been investigated at the level of the secondary, tertiary, and quaternary structure of the protein by spectroscopic and hydrodynamic techniques. The results agree with the previously identified stabilization of the enzyme but show for the first time that the protein dimer is also stabilized and suggest that the E. coli dehydroquinase subunit may be bilobal.

Circular Dichroism↗
PubMed1993

Characterization of the solution properties and conformation of pneumolysin, the membrane-damaging toxin of Streptococcus pneumoniae.

Pneumolysin is a membrane-damaging toxin produced by Streptococcus pneumoniae. In order to understand fully the mode of action of this toxin, it is necessary to have an appreciation of the size, self-association behaviour and solution conformation of pneumolysin. A combination of analytical ultracentrifugation methodologies has shown that pneumolysin lacks self-association behaviour in solution and has provided a weight-average M(r) (M omega) of 52,000 +/- 2000, which was in agreement with that derived from the amino acid sequence. By determining a sedimentation coefficient (S20,w0) of 3.35 +/- 0.10 S, it was possible to suggest a model for the gross solution conformation of pneumolysin monomers. Spectroscopic methods provide additional secondary and tertiary structure information.

Amino Acids↗
PubMed1993

The multicatalytic proteinase complex (proteasome): structure and conformational changes associated with changes in proteolytic activity.

The multicatalytic proteinase complex or proteasome is a high-molecular-mass multisubunit proteinase which is found in the nucleus and cytoplasm of eukaryotic cells. Electron microscopy of negatively stained rat liver proteinase preparations suggests that the particle has a hollow cylindrical shape (approximate width 11 nm and height 17 nm using methylamine tungstate as the negative stain) with a pseudo-helical arrangement of subunits rather than the directly stacked arrangement suggested previously. The side-on view has a 2-fold rotational symmetry, while end-on there appears to be six or seven subunits around the ring. This model is very different from that proposed by others for the proteinase from rat liver but resembles the structure of the simpler archaebacterial proteasome. The possibility of conformational changes associated with the addition of effectors of proteolytic activity has been investigated by sedimentation velocity analysis and dynamic light-scattering measurements. The results provide the first direct evidence for conformational changes associated with the observed positive co-operativity in one component of the peptidylglutamylpeptide hydrolase activity as well as with the stimulation of peptidylglutamylpeptide hydrolase activities by MnCl2. In the latter case, there appears to be a correlation between changes in the shape of the molecule and the effect on activity. KCl and low concentrations of SDS may also act by inducing conformational changes within the complex. Sedimentation-velocity measurements also provide evidence for the formation of intermediates during dissociation of the complex by urea, guanidinium chloride or sodium thiocyanate. Dissociation of the complex either by these agents or by treatment at low pH leads to inactivation of its proteolytic components. The results suggest that activation and inhibition of the various proteolytic activities may be mediated by measurable changes in size and shape of the molecules.

Animals↗
PubMed1992

T cell responses to the human papillomavirus type 16 E7 protein in mice of different haplotypes.

The response of murine T cells to the E7 molecule of human papillomavirus type 16 (HPV-16) was studied using eight different mouse strains of six distinct H-2 haplotypes. HPV-16 E7 protein was prepared as a fusion protein with glutathione-S-transferase, purified by affinity chromatography and used for immunization. Cells from the lymph nodes were cultured with whole fusion protein, glutathione-S-transferase or HPV-16 E7 protein synthetic peptides. All the mouse strains tested, with the exception of BALB/c, recognized the E7 molecule, as evidenced by a proliferative response to at least two of the peptides. The profile of responses to peptides varied between and within a strain, but five distinct immunodominant regions could be identified. These regions were defined on the basis of a reaction to one or more peptides in a given part of the E7 molecule by at least four strains. The five regions were encompassed by amino acid residues 1 to 9, 17 to 32, 42 to 59, 62 to 77 and 87 to 98. The findings suggest that in an outbred population, such as man, the E7 molecule of HPV-16 would be recognized by a large proportion of the population. However, the poor response of two mouse strains [B10.RIII (71NS) and BALB/c] could also have a corollary in man.

Animals↗
PubMed1991

A folded (10 S) conformer of myosin from a striated muscle and its implications for regulation of ATPase activity.

Myosin from the striated adductor muscle of the scallop Pecten maximus is shown to fold into a compact 10 S conformer under relaxing conditions, as has been characterized for smooth and non-muscle myosins. The folding transition is accompanied by the trapping of nucleotide at the active site to give a species with a half-life of about an hour at 20 degrees C. Ca2+ binding to the specific, regulatory sites on a myosin head promotes unfolding to the extended 6 S conformer and activates product release by 60-fold. The unfolding transition, however, remains much slower than the contraction-relaxation cycle of scallop striated muscle and could not play a role in the regulation of these events. The dissociation of products from myosin heads in native thick filaments is Ca2(+)-regulated, but under relaxing conditions the nucleotide is released at least an order of magnitude faster than from the 10 S monomeric myosin, at a rate similar to that observed with heavy meromyosin. Thus, there is no evidence for any intermolecular interaction between neighbouring molecules in the filament analogous to the head-neck intramolecular interaction in the 10 S conformer. It is possible that the 10 S myosin state represents an inert form involved in the control of filament assembly during muscle growth and development. Removal of regulatory light chains or labelling the reactive heavy chain thiol of myosin prevents, or at least disfavours, formation of the folded 10 S conformer and allows separation of the modified protein from the native molecules.

Adenosine Triphosphate↗
PubMed1991

Components of the multicatalytic proteinase complex.

The multicatalytic proteinase complex is a high molecular weight nonlysosomal proteinase. Kinetic studies of the proteolytic activities of the complex have shown that there are at least three distinct types of catalytic centre, each of which has a different specificity. All of the activities can be inhibited by the serine protease inhibitor 3,4-dichloroisocoumarin. Viewed under the electron microscope, the multicatalytic proteinase purified from rat liver appears to have a hollow cylindrical structure. It is composed of many different types of subunit and on two-dimensional polyacrylamide gels gives rise to a complex pattern of about 20 spots with pI values ranging between 5 and 8.5 and molecular masses between 22 and 34 kDa. Immunoblot analysis has shown that many of the major polypeptides are antigenically distinct. However, there are some relationships between the proteinase polypeptides. For example, although N-terminal sequences of five of the polypeptides are unique, they show considerable sequence similarity suggesting that these proteins are encoded by members of the same gene family. Also, there is some cross-reactivity between certain polypeptides when blots are probed with affinity purified, subunit-specific antisera. In addition to the variety of polypeptide components of the proteinase, a small RNA species (80 nucleotides) can be found associated with the complex even after purification by chromatographic procedures.

Animals↗
PubMed1990

Self-interaction of dynein from Tetrahymena cilia.

The molecular mass (Mr) and enzymic activity of the larger dynein species from Tetrahymena thermophila has been studied in the high (600 mM) to low (40 mM) ionic strength range. The apparent Mr is found to vary with both ionic strength (by sedimentation velocity and quasi elastic light scattering analysis) and with protein concentration at low ionic strength (by sedimentation equilibrium analysis). These data indicate a strong self-interaction, resulting in dimer formation under low salt conditions. There is no evidence for the formation of species of higher than dimeric mass. A molecular mass for the dynein monomer of 1.64 x 10(6) daltons has been determined, a value rather lower than previous published estimates. The ATPase activity of dynein increases with increasing ionic strength. The possible relationship between this effect and the self-association phenomenon is discussed.

Adenosine Triphosphatases↗
PubMed1986

The reconstruction of myosin filaments in rabbit psoas muscle from solubilized myosin.

Using rabbit psoas muscle strips, A-bands with their myosin-containing thick filaments have been substantially reconstructed in situ (as judged by electron and light microscopy and by low-angle X-ray diffraction analysis) after prior solubilization of the myosin filaments in high ionic strength potassium phosphate solution. The maintenance of a very high local concentration of soluble myosin, by means of a closely apposed artificial semi-permeable membrane is necessary for reconstruction of full-length filaments. This reconstruction effect can be totally abolished by pre-glycerolation of the muscle, or (reversibly) by pre-depletion of Ca2+. Reconstruction at longer sarcomere lengths (greater than 2.6 micron) is anomalous, part-length 'stub filaments' being formed, with their stub tails projecting out from the I-Z-I lattice. A model is proposed to explain this reconstruction effect.

Animals↗
PubMed1984

Modulation of myosin filament conformation by physiological levels of divalent cation.

The effect of divalent cation, in particular Mg2+, on the properties of synthetic myosin filaments has been studied; and substantial changes in sedimentation and light scattering demonstrated to occur in the physiological range of free Mg2+. A pre-requisite for these studies has been the definition of a modified method for the preparation of myosin in highly monodisperse filament form, rigorously free from thin filament proteins. The sedimentation coefficient at infinite dilution shows a large increase (169 S to 193 S) in the range 0.2 mM to 3 mM in Mg2+. The anomalous frictional increment found for these filaments is thus substantially reduced. The concentration dependence (ks), however, shows a substantial decrease (470 ml/g to 334 ml/g) in the same range of Mg2+, and the calculated filament molecular weight is virtually unchanged. A change in the filament conformation is thus indicated. This is confirmed by an analysis of the turbidity of the filaments in the centrifuge cell, which shows a similar increase in response to the addition of Mg2+. These effects have been found to be independent of ionic strength (0.07 to 0.11), pH (7.0 to 7.6), the presence of MgATP or the presence of low levels of Ca2+ (approximately 100 microM). These effects studied indicate the action of Mg2+ through a low-affinity binding site (Kd approximately 1.5 X 10(-3) M). We consider that a significant change in crossbridge conformation can adequately explain these changes in physical and enzymic properties. A provisional model is proposed, in which the effect of Mg2+ is to bring the crossbridges into closer proximity to the filament shaft.

Animals↗
PubMed1984

Symmetry and self-assembly in vertebrate A-filaments.

The myosin-containing A-filaments of vertebrate skeletal muscle contain 294 myosin molecules packed to give overall 3-fold rotational symmetry, as illustrated by the fraying of the filament into 3 sub-filaments ( Maw and Rowe, 1980). Further studies on slightly frayed filaments are consistent with a highly linear arrangement of these sub-filaments, at least in the major part of the cross-bridge region where sub-filaments can be observed. Isolated filaments have an unusual hydrodynamic property in the form of an anomalous frictional increment. This property is as yet unexplained; it may possibly be related to flow-induced cyclic movements in the myosin heads. Self-assembly of A-filaments in vitro to correct length and width has yet to be achieved. We have found however that under certain exactly defined conditions a very accurate reconstruction of both filaments and A-band can be accomplished in situ. Solubilisation of the myosin in chloride-free medium and maintenance of a high local myosin concentration are absolute requirements. Reconstruction is either abolished or modified by preglycerolation or at longer sarcomere length. It is argued that these results suggest a role for the actin filament lattice in myosin assembly, and imply that myosin assembly in the M-line region may be separable from myosin assembly in the cross-bridge region.

Animals↗
PubMed1983

Further evidence for a flexible and highly expanded spheroidal model for mucus glycoproteins in solution.

The flexible and greatly expanded roughly spherical model for mucus glycoproteins proposed earlier, on the basis of hydrodynamic and n.m.r. data, is supported by new hydrodynamic results on a bronchial glycoprotein from a cystic-fibrosis patient. Furthermore, images from electron microscopy of this molecule and a lower-molecular-weight mucus glycoprotein (which closely resembles a glycopolypeptide) appear to be at least consistent with this model.

Cystic Fibrosis↗