Biomedical subjects

Gundo Diedrich

Publications and source records attributed to Gundo Diedrich.

3 recordsLinked to original sources

PubMed2006

How does hepatitis C virus enter cells?

Hepatitis C virus (HCV) exists in different forms in the circulation of infected people: lipoprotein bound and lipoprotein free, enveloped and nonenveloped. Viral particles with the highest infectivity are associated with lipoproteins, whereas lipoprotein-free virions are poorly infectious. The detection of HCV's envelope proteins E1 and E2 in lipoprotein-associated virions has been challenging. Because lipoproteins are readily endocytosed, some forms of HCV might utilize their association with lipoproteins rather than E1 and E2 for cell attachment and internalization. However, vaccination of chimpanzees with recombinant envelope proteins protected the animals from hepatitis C infection, suggesting an important role for E1 and E2 in cell entry. It seems possible that different forms of HCV use different receptors to attach to and enter cells. The putative receptors and the assays used for their validation are discussed in this review.

Hepacivirus↗

PubMed2002

A characterization of the lumenal region of human tapasin reveals the presence of two structural domains.

Tapasin is a type I membrane glycoprotein involved with other accessory proteins in the assembly of class I MHC-beta(2)m-peptide complexes in the endoplasmic reticulum. We have probed the three-dimensional structure of the lumenal region of human tapasin (residues 1-392) tagged with a (His)(6) sequence at its C-terminus using biochemical and biophysical techniques. The far-UV circular dichroism spectrum revealed that tapasin possesses well-defined secondary structural elements corresponding predominantly to beta-sheets. A thermal denaturation curve recorded at 216 nm showed a midpoint transition centered at approximately 45 degrees C. Sedimentation analysis showed that tapasin is monomeric in solution with a sedimentation coefficient, S degrees (20,w), of 2.68 S. This value of S degrees (20,w) combined with the value of the molar mass obtained by MALDI mass spectrometry (44.2 kDa) yielded a frictional ratio, f/f(0), of 1.47. Assuming tapasin is a prolate ellipsoid, we calculated an apparent length of 22.5 nm and a diameter of 2.62 nm, consistent with an elongated molecular shape. Controlled proteolysis using various enzymes revealed that a narrow region of tapasin near residue 90 is highly susceptible to digestion, resulting in two fragments that are resistant to further cleavage. The identity of these fragments was determined by amino acid sequencing and MALDI mass spectrometry and revealed a 9 kDa N-terminal fragment and a 34 kDa C-terminal fragment. Collectively, these results suggest that tapasin is comprised of two core domains of different sizes loosely linked by a flexible region.

Antiporters↗

PubMed2002

Identification of specific glycoforms of major histocompatibility complex class I heavy chains suggests that class I peptide loading is an adaptation of the quality control pathway involving calreticulin and ERp57.

Glycosylation analysis was used to probe the sequence of events accompanying the binding of antigenic peptides to the major histocompatibility complex class I heavy chains. Free heavy chains were isolated from the beta(2)-microglobulin-negative cell line Daudi and from the B-lymphoblastoid cell line Raji. Heavy chains were also isolated from Raji cells in multimolecular complexes (peptide loading complexes) containing the transporter associated with antigen processing, tapasin and ERp57 with and without the lectin-like folding chaperone, calreticulin. Calreticulin is a soluble protein that recognizes primarily the terminal glucose of Glc(1)Man(7-9)GlcNAc(2) glycans. This paper shows that monoglucosylated glycoforms of heavy chain, which exist transiently in the endoplasmic reticulum in the initial stages of the glycosylation processing pathway, are present in the peptide loading complex. The data are consistent with a model in which the release of peptide-loaded major histocompatibility complex class I molecules from calreticulin, induced by deglucosylation of the heavy chain N-linked glycan, signals the dissociation of the complex. This is consistent with the hypothesis that the class I loading process is an adaptation of the quality control mechanism involving calreticulin and ERp57.

Calreticulin↗