Delivery of nascent MHC class II-invariant chain complexes to lysosomal compartments and proteolysis of invariant chain by cysteine proteases precedes peptide binding in B-lymphoblastoid cells.

Abstract The intracellular trafficking, proteolysis, and dissociation of invariant chain (li) associated with nascent class II molecules was examined in B-lymphoblastoid cells. Metabolic labeling and Percoll gradient centrifugation was used to assess the kinetics of delivery and processing of class II-li complexes within the endocytic pathway. Catabolism of class II-li complexes rapidly followed their delivery from post-Golgi compartments to dense lysosome-like compartments distinct from early and late endosomes. Direct peptide binding assays revealed that class II molecules associated with even small N-terminal fragments of li failed to bind peptide. Cysteine protease inhibitors alone blocked li proteolysis/dissociation and accumulation of class II-li biosynthetic intermediates within lysosome-containing compartments. Active-site labeling of cysteine proteases in B cells was used to identify cysteine proteases capable of mediating li proteolysis within endosomal compartments. Our results indicate rapid, possibly direct, transport of nascent class II-li complexes from the Golgi/trans-Golgi network to dense lysosomal compartments wherein cysteine protease(s), likely including cathepsin B, mediate complete removal of li. Inhibition of cysteine protease activity results in the accumulation of incompletely processed class II-li complexes, which lack peptide binding ability, within lysosomal compartments.</jats:p

Human Ia alpha- and beta-chains are sulfated.

Abstract The human Ia antigens (DR, DQ, and DP), determined by genes with the HLA complex, are heterodimers consisting of a 34,000-Da alpha-chain glycoprotein and a 29,000-Da beta-chain glycoprotein. During the course of studies characterizing a recently described sulfated proteoglycan that is specifically associated with Ia, we discovered that there were also nonproteoglycan sulfated components present in the Ia immunoprecipitates. One-dimensional sodium dodecyl sulfate-gel analysis of these latter sulfated components derived from both DR and DQ immunoprecipitates indicated that these components have mobilities indistinguishable from conventional Ia alpha and beta glycoproteins. Two-dimensional gel analysis confirmed these findings and revealed that Ia-associated invariant proteins are sulfated as well. The sulfate moiety was not removed by endoglycosidase F treatment, suggesting that the protein portion of the molecule was sulfated. These results indicate that Ia alpha-, beta-, and invariant chains can be sulfated and raise the possibility that sulfation may play a role in the physiology of Ia molecules.</jats:p

Radiation Induced Catalytic Dechlorination of Hexachlorobenzene on Oxide Surfaces

Radiation induced catalytic dehalogenation of hexachlorobenzene (HCB) adsorbed to alumina (Al2O3), silica (SiO2), titania (TiO2), zirconia (ZrO2), and a commercially available zeolite has been studied using Cobalt-60 (60Co) as a radiation source. Solid-particulate samples were irradiated over a dose range of 0−58 kGy, and the chemical changes were monitored using Fourier transform infrared diffuse reflectance (FTIR-DR) and gas chromatography with electron capture detection (GC-ECD). The extent of HCB degradation on the metal oxides was found to increase dramatically in samples evacuated under vacuum, pointing to the competitive scavenging of conduction band electrons by surface adsorbed species, primarily oxygen. Coadsorbed water diminished HCB conversion on all oxides but to a greater degree on alumina. HCB degradation on metal oxides was found to be highly dependent upon the conduction band energy of the support material, thus confirming the occurrence of ultra-band-gap excitation and charge separation in irradiated oxides. Higher yields of dechlorination products were witnessed in alumina and silica samples. Zeolite, titania, and zirconia were also found to be inefficient in promoting radiation induced catalysis. The absence of oxidation products in the irradiated HCB/oxide samples suggests the inaccessibility of holes to undergo interfacial charge transfer with the organic substrate