Biosynthesis of intestinal microvillar proteins. Dimerization of aminopeptidase N and lactase-phlorizin hydrolase.

The pig intestinal brush border enzymes aminopeptidase N (EC 3.4.11.2) and lactase-phlorizin hydrolase (EC 3.2.1.23-62) are present in the microvillar membrane as homodimers. Dimethyl adipimidate was used to cross-link the two [35S]methionine-labeled brush border enzymes from cultured mucosal explants. For aminopeptidase N, dimerization did not begin until 5-10 min after synthesis, and maximal dimerization by cross-linking of the transient form of the enzyme required 1 h, whereas the mature form of aminopeptidase N cross-linked with unchanged efficiency from 45 min to 3 h of labeling. Formation of dimers of this enzyme therefore occurs prior to the Golgi-associated processing, and the slow rate of dimerization may be the rate-limiting step in the transport from the endoplasmic reticulum to the Golgi complex. For lactase-phlorizin hydrolase, the posttranslational processing includes a proteolytic cleavage of its high molecular weight precursor. Since only the mature form and not the precursor of this enzyme could be cross-linked, formation of tightly associated dimers only takes place after transport out of the endoplasmic reticulum. Dimerization of the two brush border enzymes therefore seems to occur in different organelles of the enterocyte.

Chemically attenuated larvae of S. mansoni as a novel tool in schistosomiasis research: 2. Chemical attenuation of cercariae by diimidoesters.

A novel approach to chemically attenuate cercariae of S. mansoni is presented. The method utilizes the biologically active surface proteins/glycoproteins which are essential for the survival of the organism as a target for inactivation. The inactivation was achieved by reaction with 0.01 M dimethyl adipimidate, dimethyl pimelimidate or dimethyl suberimidate at pH 8.5. The cercariae lost their viability, but retained the ability to exclude trypan blue for up to 2 years when stored at 4 degrees C in a manner similar to live cercariae and in contrast to dead cercariae which took up the dye immediately. In addition, the attenuated cercariae reacted with monoclonal and polyclonal antischistosome antibodies in an indirect immunofluorescence assay indicating the retention and preservation of surface antigens after attenuation. The immunochemical reactivity of the attenuated cercariae was preserved after storage for 2 years at 4 degrees C as shown by reaction with antisera from infected mice and rats in IIF assay. Attenuated cercariae revealed the presence of antischistosome antibodies as early as one week after infection in mice and rats. The presence of receptors for the Fc portion of human IgG on the attenuated cercariae interfered in their use as an immunodiagnostic reagent for human schistosomiasis. The attenuated cercariae were also used to screen cultures for monoclonal antischistosome antibodies. Preliminary results indicated that immunization with attenuated cercariae was capable of imparting protective immunity in mice.

Chemically attenuated larvae of S. mansoni as a novel tool in schistosomiasis research: 2. Chemical attenuation of cercariae by diimidoesters

A novel approach to chemicallu attenuate cercariae fo S. mansoni is presented. The method utilizes the biologically active surface proteins/glycoproteins which are essential for the survival of the organism as a target for inactivation. The inactivation was achieved by reaction with 0.01 M dimethil adipimidate, dimethyl pimelimidate or dimethyl suberimidate at pH 8.5. The cercariae lost their viability, but retained the ability to exclude trypan blue for up to 2 years when stored at 4-C in a manner similar to live cecariae and in contrast to dead cercariae witch took up the dye immediately. In addition, the attenuated cercariae reacted with monoclonal and policlonal antischistosome antibodies in an indirect immunofluorescence assay indacting the retention and preservation of surface antigens after attenuation. The immunochemical reactivity of the attenuated cercariae was preserved after storage for 2 years at 4-C as shown by reaction with antisera from infected mice and rats in IIF assay. Attenuated cercariae revealed the presence of antischistosome antibodies as early as one week after infection in mice and rats. The presence of receptors for the Fc portion of human IgG on the attenuated cercariae interfered in their use as an immunodiagnostic reagent for human schistosomiasis. The attenuated cercariae were also used to screen cultures for monoclonal antischistosome antibodies. preliminary results indicated that immunozation with attenuated cercariae was capable of imparting protective immunity in mice

Cross-linking of Newcastle disease virus (NDV) proteins.

The proxomity and spatial relationships of the structural proteins of Newcastle disease virus (NDV) were studied by chemical cross-linking with a series of imidoesters. When the virions were reacted by the cross-linker with a distance 6.1A or longer between the functional groups and analyzed by polyacrylamide gel electrophoresis, remarkable changes were observed in the migration patterns of the viral proteins. The most striking one was the extensive decrease in the intensity of the M protein band, and although not so strikingly, glycoprotein and nucleocapsid protein bands were reduced significantly. Instead, several protein complexes appeared at and near the top of the gels. The protein complexes formed by a reversible cross-linker, dimethyl-3,3'-dithiobispropionimidate (DTBP), were analyzed by two dimensional electrophoresis; the complexes on the first-dimension cylindrical gels were cleaved by reduction with 2-mercaptoethanol and electrophoresed laterally on the second-dimension slab gels. The results indicated that homodimers of glycoprotein, nucleocapsid protein and M protein were generated under the condition of the most gentle cross-linking employed. At the same time, however, trimer and higher homopolymers of M protein were already detectable. Under the more extensive conditions, the bulk of M protein was cross-linked to form a large protein complex with very high molecular weight. Further, small but significant amounts of glycoprotein and nucleocapsid protein were always detected in this complex. These results suggest that M protein may be present in the virion in close enough proximity to interact with each other and may further have some interactions with glycoprotein and nucleocapsid protein. On the basis of these findings possible roles of M protein in virus assembly were discussed.