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S Cusack

Publications and source records attributed to S Cusack.

At least 109 records · Page 6Linked to original sources
PubMed1987

Direct measurement of hydration-related dynamic changes in lysozyme using inelastic neutron scattering spectroscopy.

Inelastic neutron scattering spectroscopy is used to investigate dynamic changes in lysozyme powder at two different low D2O hydrations (0.07g D2O/g protein and 0.20 g D2O/g protein). In the higher hydration sample, the inelastic scattering between 0.8 and 4.0 cm-1 energy transfer is increased and the elastic scattering is decreased. The decreased elastic scattering suggests increased atomic amplitudes of motion and the increased 0.8 to 4.0 cm-1 scattering suggests increased motions in this frequency range. Comparison with normal mode models of lysozyme dynamics shows that the inelastic difference occurs in the frequency region predicted for the lowest frequency, largest amplitude, global modes of the molecular [M. Levitt, C. Sander and P.S. Stern, J. Mol. Biol. 181, 423 (1985). B. Brooks and M. Karplus, Proc. Natl. Acad. Sci (U.S.A) 82, 4995 (1985), R.E. Bruccoleri, M. Karplus and J.A. McCammon, Biopolymers 25 1767 (1986)]. Our results are consistent with a model in which an increased number of low frequency global modes are present in the higher hydrated sample.

Energy Transfer↗
PubMed1986

Electron microscopy of the low pH structure of influenza virus haemagglutinin.

Influenza virus haemagglutinin mediates infection of cells by fusion of viral and endosomal membranes, triggered by low pH which induces a conformational change in the protein. We report studies of this change by electron microscopy, neutron scattering, sedimentation and photon correlation on X-31 (H3N2) haemagglutinin, both intact and bromelain cleaved, in various assemblies. HAs in all preparations showed a thinning at low pH, and a marked elongation which was removed on tryptic digestion, revealing altered features in the remaining stem portion of the molecule. A tentative model of the change is proposed, with reference to the known X-ray structure at neutral pH, in which major changes occur in the stem tertiary structure, while the top portion is only affected in its quaternary structure.

Animals↗
PubMed1985

Structure and composition of influenza virus. A small-angle neutron scattering study.

A detailed analysis is presented of the small-angle neutron scattering curves of homogeneous solutions of influenza B virus, both intact and after treatment with bromelain, which removes the external glycoprotein spikes. The two sets of data are consistent with the following low-resolution structure: the virus particles are spherical, about 1200 A in diameter and of Mr about 180 X 10(6). The lipid bilayer is centred at a radius of 425 A, is 40 A to 50 A thick and constitutes 25% to 28% of the virus mass. The surface glycoproteins, predominantly haemagglutinin, contribute 40% to 46% of the total mass. Surprisingly little protein is found in the interior of the virus. It is suggested that the reason for this is that many particles do not contain the full complement of ribonucleoprotein complexes. These results are in good agreement with recent scanning transmission electron microscopic measurements of molecular mass and cryo-electron microscopic observations of the same preparations. Appendix 1 describes a new method of deriving spherical shell models from contrast variation neutron scattering data on viruses, in which scattering curves from all measured contrasts are used simultaneously. There is also a discussion of the assumptions and limitations implicit in the structural interpretation of such models, with emphasis on viruses containing lipid bilayers. Appendix 2 examines the effect on the scattering curves of various arrangements of the surface glycoproteins.

Bromelains↗
PubMed1985

Three-dimensional molecular shape determination from a limited number of projections.

A real space method allowing the reconstruction of negatively stained crystalline objects from a limited number of projections is presented. The method is based on the assumption that only two density levels are required to describe an ideally negatively stained object (that of the volume occupied by the object and that of the volume occupied by the stain). The method is illustrated by the reconstruction of the asymmetric unit of catalase microcrystals using only the three principal projections. It is shown that other projections can then be predicted to a good approximation.

Animals↗
PubMed1984

Low resolution structure of the influenza C glycoprotein determined by electron microscopy.

The influenza C glycoprotein is clearly seen to be a trimer in specimens prepared with uranyl stains. Three-dimensional reconstructions from naturally occurring hexagonal arrays show that at low resolution (approximately 30 A) the influenza C glycoprotein exhibits similar features to the haemagglutinin glycoprotein of influenza A. Both have a triangular stalk near the membrane. Further from the membrane, the stalk becomes broader and the monomers more separated, leaving an open centre. The molecule narrows at the top. The regions of greatest contact between adjacent trimers in the arrays are situated nearer the distal end of the molecule. These contact zones can be related to equivalent zones on the influenza A haemagglutinin. Differences between the structure of the influenza A haemagglutinin glycoprotein determined by X-ray analysis and reconstructions of the influenza C glycoprotein are greatest at either end of the molecule, where the reconstructions are least reliable. Ordered glycoprotein arrays have not been observed on influenza C virions incubated at low pH. The staining patterns of glycoproteins on intact virions are essentially determined by the pH at which the virus is incubated, and the stain type, but not the pH of the stain.

Humans↗
PubMed1983

Structure of the Top a-t component of alfalfa mosaic virus. A non-icosahedral virion.

Neutron-scattering in combination with quasi-elastic light-scattering and electron microscopy was used to derive a model for the capsid structure of the Top a-t component of alfalfa mosaic virus (AMV-Ta-t). In the electron microscope, AMV-Ta-t appears as an irregular ellipsoidal particle with apparent dimensions 275 (+/- 31) A X 225 (+/- 22) A. Assuming that the particles are monodisperse, model calculations show that the neutron-scattering data are best explained by an oblate ellipsoidal shape for the virion with external dimensions 284 A X 284 A X 216 A. Based on this result, and in combination with the known composition of the virion, it is suggested that the capsid structure could be based on a deltahedron with 52 pointgroup symmetry and comprising 120 subunits. Such a model would imply a greater deviation from equivalent subunit interactions than normally necessary in icosahedral capsids. The neutron and photon correlation data, however, do not allow us to rule out the possibility that Top a-t is a slightly polydisperse preparation of irregular prolate shapes with mean dimensions 312 A X 232 A X 232 A. Both possibilities support the concept of alfalfa mosaic virus coat protein being capable of a wide range of intersubunit interactions, this flexibility resulting in considerable polymorphism in capsid structures.

Capsid↗
PubMed1983

Solution scattering study on the structure of alfalfa mosaic virus strain VRU.

Neutron-scattering with contrast variation has been used to derive a model for the radial distribution of protein and RNA in the VRU strain of alfalfa mosaic virus. The RNA is distributed uniformly throughout the interior of the capsid up to a radius of 65 A and the protein coat extends from 65 to 100 A. It was found necessary to distinguish between two regions within the protein coat: one with mainly hydrophobic amino acids and another with more hydrophylic amino acids. Only a very small part of the protein penetrates into the RNA. Using X-ray scattering, no indication was found for long or short-range order in the packing of the RNA in the virion.

Medicago sativa↗
PubMedDate not supplied

Olfactory function in people with genetic risk of dementia.

BACKGROUND: Screening for sensorial impairment is a secondary objective in the context of neurodegenerative diseases, including dementias. For example, olfactory dysfunction is among the first signs of Alzheimer's disease. There has been no study of olfactory function in Irish subjects at risk of dementia. AIM: To investigate olfactory function in non-demented Irish persons, who carry genetic risk factors for dementia. METHODS: Thirty-eight Irish adult subjects, who are at risk of dementia, were recruited. Cognitive performance and olfactory function were assessed and apolipoprotein E (APOE) genotype determined. RESULTS: Three and six subjects had a Mini Mental State Examination (MMSE) and Brief Smell Identification Test (B-SIT) score, respectively, outside the normal range. While five out of the fifteen epsilon-4 allele positive subjects had B-SIT scores outside the normal range, only one out of the twenty-three epsilon-4 allele negative subjects had; the difference in this frequency was significant (P=0.025). There was no significant difference (P=0.266) in the frequency of abnormal MMSE scores between epsilon-4 allele groups. CONCLUSION: Further investigation is required to explore the reasons for the higher prevalence of olfactory dysfunction in epsilon-4 allele positive subjects.

Age Distribution↗