60 research outputs found
Relativistic theory of tidal Love numbers
In Newtonian gravitational theory, a tidal Love number relates the mass
multipole moment created by tidal forces on a spherical body to the applied
tidal field. The Love number is dimensionless, and it encodes information about
the body's internal structure. We present a relativistic theory of Love
numbers, which applies to compact bodies with strong internal gravities; the
theory extends and completes a recent work by Flanagan and Hinderer, which
revealed that the tidal Love number of a neutron star can be measured by
Earth-based gravitational-wave detectors. We consider a spherical body deformed
by an external tidal field, and provide precise and meaningful definitions for
electric-type and magnetic-type Love numbers; and these are computed for
polytropic equations of state. The theory applies to black holes as well, and
we find that the relativistic Love numbers of a nonrotating black hole are all
zero.Comment: 25 pages, 8 figures, many tables; final version to be published in
Physical Review
Shiga Toxin Binding to Glycolipids and Glycans
Background: Immunologically distinct forms of Shiga toxin (Stx1 and Stx2) display different potencies and disease outcomes, likely due to differences in host cell binding. The glycolipid globotriaosylceramide (Gb3) has been reported to be the receptor for both toxins. While there is considerable data to suggest that Gb3 can bind Stx1, binding of Stx2 to Gb3 is variable. Methodology: We used isothermal titration calorimetry (ITC) and enzyme-linked immunosorbent assay (ELISA) to examine binding of Stx1 and Stx2 to various glycans, glycosphingolipids, and glycosphingolipid mixtures in the presence or absence of membrane components, phosphatidylcholine, and cholesterol. We have also assessed the ability of glycolipids mixtures to neutralize Stx-mediated inhibition of protein synthesis in Vero kidney cells. Results: By ITC, Stx1 bound both Pk (the trisaccharide on Gb3) and P (the tetrasaccharide on globotetraosylceramide, Gb4), while Stx2 did not bind to either glycan. Binding to neutral glycolipids individually and in combination was assessed by ELISA. Stx1 bound to glycolipids Gb3 and Gb4, and Gb3 mixed with other neural glycolipids, while Stx2 only bound to Gb3 mixtures. In the presence of phosphatidylcholine and cholesterol, both Stx1 and Stx2 bound well to Gb3 or Gb4 alone or mixed with other neutral glycolipids. Pre-incubation with Gb3 in the presence of phosphatidylcholine and cholesterol neutralized Stx1, but not Stx2 toxicity to Vero cells
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