Differential scanning calorimetry ͑DSC͒ has been used to evaluate the average enthalpy of desorption of the water of primary hydration bound to wet-spun films of potassium hyaluronate ͑KHA͒ and CsDNA. The enthalpies were measured to be 0.24Ϯ0.08 eV/H 2 O molecule for KHA and 0.32Ϯ0.10 eV/H 2 O molecule for CsDNA. A Kissinger analysis was used to extract the net activation energy (0.61Ϯ0.04 eV͒ for the desorption of this water from KHA by analyzing DSC data acquired at different heating rates. The average effective force constants at 295 K of this water bound to KHA (63Ϯ3 dyn/Å͒ and NaDNA (17Ϯ4 dyn/Å͒ are determined from Rayleigh scattering of Mossbauer radiation data ͓G. Albanese, A. Deriu, F. Cavatorta, and A. Rupprecht, Hyperfine Interact. 95, 97 ͑1995͔͒ via a harmonic approximation.
Epstein-Barr virus (EBV), a herpesvirus with oncogenic potential, is camouflaged with glycoprotein 350/220, which mimics the human ligand C3dg and thereby binds to and exploits complement receptor type 2 (CR2; CD21), the EBV receptor. It has not been possible to determine the role of CR2 during postbinding events of viral infection because all B lymphocytes express endogenous CR2, precluding an informative study of receptor mutants. We have overcome this obstacle through creation of a novel experimental system based on molecular dissection of the ligand-binding domains of human CR2 and murine CR2. Our results demonstrate first, that two discontinuous amino acid substitutions within the ligand-binding domain of murine CR2 render it capable of mediating EBV infection of human B-lymphoblastoid cells, and second, that the specific role of CR2 during EBV infection is to capture virions at the cell surface, after which cofactors not associated with CR2 mediate postbinding events. These are the first studies to be described in which a cell that is normally susceptible to viral infection can be manipulated so as to direct entry of virions via recombinant or endogenous receptors.
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