Altering the structures of 3D supramolecular assemblies from melamine and cyanuric acid derivatives in water.

Herein, we obtained two supramolecular assemblies with layered structures from melamine, -methylmelamine, and hexynyl-cyanuric acid in water. By combination of X-ray diffraction, electron microscopy, and molecular dynamics studies, we found that introducing one methyl group in melamine alters the arrangement of the layers in these structures.

A novel mammalian endoplasmic reticulum ubiquitin ligase homologous to the yeast Hrd1.

The yeast hHrd1 is a ubiquitin-protein ligase (E3) involved in ER-associated degradation. It was originally identified by genetic methods as an E3 of the yeast cholesterol biosynthetic enzyme HMG-CoA reductase (HMGR). We report the identification and cloning of a human homologue of Hrd1 (hHrd1).

A role for a novel luminal endoplasmic reticulum aminopeptidase in final trimming of 26 S proteasome-generated major histocompatability complex class I antigenic peptides.

Peptides presented to cytotoxic T lymphocytes by the class I major histocompatability complex are 8-11 residues long. Although proteasomal activity generates the precise C termini of antigenic epitopes, the mechanism(s) involved in generation of the precise N termini is largely unknown. To investigate the mechanism of N-terminal peptide processing, we used a cell-free system in which two recombinant ornithine decarboxylase (ODC) constructs, one expressing the native H2-K(b)-restricted ovalbumin (ova)-derived epitope SIINFEKL (ODC-ova) and the other expressing the extended epitope LESIINFEKL (ODC-LEova), were targeted to degradation by 26 S proteasomes followed by import into microsomes.

26 S proteasome-mediated production of an authentic major histocompatibility class I-restricted epitope from an intact protein substrate.

Peptides displayed on the cell surface by major histocompatibility class I molecules (MHC class I) are generated by proteolytic processing of protein-antigens in the cytoplasm. Initially, antigens are degraded by the 26 S proteasome, most probably following ubiquitination. However, it is unclear whether this proteolysis results in the generation of MHC class I ligands or if further processing is required.

Electrical sizing of particles in suspensions. II. Experiments with rigid spheres.

Experimental verification is provided for the theoretical expressions (see preceding article, I. Theory) describing the electrical processes that take place during the passage of an aqueous suspension of rigid, nonconducting spheres (ragweed pollen) through an orifice across which there exists an electrical field, for a large range of orifice dimensions; the instrumentation developed is considered in some detail. The effective length of an orifice as deduced from conductivity measurements is shown to be essentially the same as that predicted theoretically.