MAL, an Integral Element of the Apical Sorting Machinery, Is an Itinerant Protein That Cycles between the Trans-Golgi Network and the Plasma Membrane

The MAL proteolipid is a nonglycosylated integral membrane protein found in glycolipid-enriched membrane microdomains. In polarized epithelial Madin-Darby canine kidney cells, MAL is necessary for normal apical transport and accurate sorting of the influenza virus hemagglutinin. MAL is thus part of the integral machinery for glycolipid-enriched membrane–mediated apical transport. At steady state, MAL is predominantly located in perinuclear vesicles that probably arise from the trans-Golgi network (TGN). To act on membrane traffic and to prevent their accumulation in the target compartment, integral membrane elements of the protein-sorting machinery should be itinerant proteins that cycle between the donor and target compartments. To establish whether MAL is an itinerant protein, we engineered the last extracellular loop of MAL by insertion of sequences containing the FLAG epitope or with sequences containing residues that became O-glycosylated within the cells or that displayed biotinylatable groups. The ectopic expression of these modified MAL proteins allowed us to investigate the surface expression of MAL and its movement through different compartments after internalization with the use of a combination of assays, including surface biotinylation, surface binding of anti-FLAG antibodies, neuraminidase sensitivity, and drug treatments. Immunofluorescence and flow cytometric analyses indicated that, in addition to its Golgi localization, MAL was also expressed on the cell surface, from which it was rapidly internalized. This retrieval implies transport through the endosomal pathway and requires endosomal acidification, because it can be inhibited by drugs such as chloroquine, monensin, and NH4Cl. Resialylation experiments of surface MAL treated with neuraminidase indicated that ∼30% of the internalized MAL molecules were delivered to the TGN, probably to start a new cycle of cargo transport. Together, these observations suggest that, as predicted for integral membrane members of the late protein transport machinery, MAL is an itinerant protein cycling between the TGN and the plasma membrane.

A medida provisória em matéria tributária no regime da Emenda Constitucional 32/2001 : limites à edição e eficácia

"Artigo produzido com base no trabalho de conclusão do Curso de Especialização em Análise e Controle de Constitucionalidade, promovido pela Unilegis - Universidade do Legislativo em parceria com a Universidade de Brasília - UNB, como requisito para a obtenção do título de especialista. Orientador: Prof. José Geraldo de Sousa Júnior".

Dois temas importantes : biografias "não-autorizadas" e limites de citações de livros / Alaor Barbosa. --

Inclui bibliografia.

Os limites linguístico-legislativos da discricionariedade judicial / Pedro Henrique Pedrosa Nogueira. --

Inclui notas explicativas, bibliográficas e bibliografia.

Realidade e limites do arcabouço legal de prevenção, controle e fiscalização da introdução de espécies marinhas exóticas no Brasil / Anderson Eduardo Silva de Oliveira, Carlos José Saldanha Machado e Denise Setsuko Okada. --

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Os limites da política comercial da comunidade européia / Peter Gilsdort. --

Palestra realizada em 12.02.88 no Instituto Europeu da Universidade do Sarre, República Federal da Alemanha.