Solution structure of an N-capping peptide from the N-terminal leucine-repeat region of hepatitis delta antigen

Hepatitis delta virus (HDV) is a satellite virus of the hepatitis B virus (HBV) which provides the surface antigen for the viral coat. The RNA genome of HDV encodes two proteins, the small delta antigen and the large delta antigen, which differ only with the latter having an additional 19 amino acids at the C-terminus. Previously, we have shown that dAg24-50, a synthetic peptide corresponding to residues 24-50 of the N-terminal leucine-repeat region of hepatitis delta antigen, binds to the viral RNA and forms an alpha-helical conformation in TFE-containing solution. However, it exhibited low alpha-helicity (less than 5%) in the absence of TFE. In order to obtain biologically active delta antigen peptides with higher structural stability in solution, an N-capping 21-residue polypeptide corresponding to residues 24-38 of hepatitis delta antigen (dAg(Cap24-38am)) was synthesized and, surprisingly, its solution structure was found to be a stable alpha-helix (64%) by circular dichroism and 1H NMR techniques. Moreover, the structure of the capping box shows the characteristic L-shaped bend perpendicular to the helix axis. This structural knowledge provides a molecular basis for understanding the role of the N-terminal leucine-repeat region of hepatitis delta antigen and has a significant potential for the development of diagnostic and therapeutic methods for HDV.     

Lack of obvious 50 kilobase pair DNA fragments in DNA fragmentation factor 45-deficient thymocytes upon activation of apoptosis

The DNA fragmentation factor 45 (DFF45/ICAD) is a key subunit of a heterodimeric DNase complex critical for the induction of DNA fragmentation during apoptosis in vivo. To further assess the importance of DFF45 in chromosomal DNA degradation, we induced apoptosis in wild-type control and DFF45 deficient thymocytes and compared the cleavage of chromosomal DNA to 50 kilobase pair size fragments. We found that there is a lack of obvious large chromosomal DNA fragments upon treatments by various apoptotic agents in DFF45 deficient thymocytes. The major organ systems in the DFF45 mutant mice either two months or fifteen months of age appear normal. These results suggest that functional DFF45 is required for cleavage of DNA into both large size and oligonucleosomal size fragments in thymocytes during apoptosis. However, deficiency in DFF45 apparently does not significantly affect normal mouse development and tissue homeostasis.     

The effect of anisotonic media upon cellular ultra-structure in fresh and fixed rat brain

Summary When tissue slices or small blocks of unfixed rat cerebrum are incubated in various anisotonic physiological media, distinctive morphological changes are induced in glial cells, neurons, and endothelial cells. The variation in observed cellular swelling and shrinkage may be related to differences in ionic content of the cytoplasm of these cells. When HAA, glutal, and osmium tetroxide fixed tissue is incubated in this manner, only the cerebrum fixed in HAA responds to osmotic inequilibrium in a manner similar to unfixed tissue. Although HAA does not fix tissues very well, the permeability of plasma membranes in the brain appears to be less altered by HAA than by glutal or osmium tetroxide. The relationship of these findings to a demonstration of the extracellular space in HAA fixed tissues is discussed.This work was supported by grants (U-1293) from the Health Research Council of the City of New York and (NB 04161-02) from the National Institute of Neurological Disease and Blindness of the National Institutes of Health.