Degradation of apolipoprotein B-100 by lysosomal cysteine cathepsins

Although the degradation of cellular or endocytosed proteins comprises the normal function of lysosomal proteinases, these enzymes were also detected extracellularly during diseases such as atherosclerosis. Since lysosomal cysteine cathepsins were demonstrated to transform native LDL particles into a proatherogenic type, the following study was undertaken to characterize the modification of LDL particles and the degradation of apolipoprotein B-100 in more detail. LDL was incubated with cathepsins B, F, K, L, S, and V at pH 5.5 and under physiological conditions (pH 7.4) for 2 h to mimic conditions of limited proteolysis. Gel electrophoretic analysis of the degradation products revealed that cathepsin-mediated proteolysis of apolipoprotein B-100 is a fast process carried out by all enzymes at pH 5.5, and by cathepsin S also at pH 7.4. Electron microscopic analysis showed that cathepsin-mediated degradation of apolipoprotein B-100 rendered LDL particles fusion-competent compared to controls. N-Terminal sequencing of cathepsin cleavage fragments from apolipoprotein B-100 revealed an abundance of enzyme-specific cleavage sites located in almost all structurally and functionally essential regions. Since the cleavage sites superimpose well with results from substrate specificity studies, they might be useful for the development of cathepsin-specific inhibitors and substrates.

Muscle endopin 1, a muscle intracellular serpin which strongly inhibits elastase: purification, characterization, cellular localization and tissue distribution

In the present work, an endopin-like elastase inhibitor was purified for the first time from bovine muscle. A three-step chromatography procedure was developed including successively SP-Sepharose, Q-Sepharose and EMD-DEAE 650. This procedure provides about 300 microg of highly pure inhibitor from 500 g of bovine diaphragm muscle. The N-terminal sequence of the muscle elastase inhibitor, together with the sequence of a trypsin-generated peptide, showed 100% similarity with the cDNA deduced sequence of chromaffin cell endopin 1. Hence, the muscle inhibitor was designated muscle endopin 1 (mEndopin 1). mEndopin 1 had a molecular mass of 70 kDa, as assessed by both gel filtration and SDS/PAGE. According to the association rates determined, mEndopin 1 is a potent inhibitor of elastase (kass=2.41x10(7) M(-1).s(-1)) and trypsin (kass=3.92x10(6) M(-1).s(-1)), whereas plasmin (kass=1.78x10(3) M(-1).s(-1)) and chymotrypsin (kass=1.0x10(2) M(-1).s(-1)) were only moderately inhibited. By contrast, no inhibition was detected against several other selected serine proteinases, as well as against cysteine proteinases of the papain family. The cellular location of mEndopin in muscle tissue and its tissue distribution were investigated using a highly specific rabbit antiserum. The results obtained demonstrate an intracellular location and a wide distribution in bovine tissues.

Functional expression of the catalytic domains of two cysteine proteinases from Trypanosoma congolense

The catalytic domains of two closely related cysteine proteinases (CP1 and CP2) from Trypanosoma congolense, referred to as C1 and C2, were expressed as proforms in Escherichia coli (C1) and in the baculovirus system (C1 and C2). While the bacterial expression system did not allow recovery of active C1, the baculovirus system led to secretion of inactive zymogens which could be processed at acidic pH into mature enzymes. Active C1 and C2 were purified from serum-free culture supernatants by anion-exchange chromatography and characterised. Their kinetic parameters and pH activity profiles confirmed the relatedness between C2 and native CP2 (congopain). These properties also underline major functional differences between C1 and C2, that appear to relate to discrete but essential sequence differences. It is likely that these two enzymes perform distinct roles in vivo, in the parasite and/or in the host-parasite relationships.

[A new alpha chain of jacalin from two wild species of jack-fruit seeds]

Jacalins, from jack-fruit seeds of 2 wild species (Artocarpus asperulus, Artocarpus masticata) were purified by mucine-sepharose 4B affinity chromatography. The alpha and beta chains were separated by reverse phase high pressure liquid chromatography (HPLC). Analysis by HPLC with a C8 column and the determination of the N-terminal sequence of the alpha-chain of these jacalins allowed the identification of a new alpha-chain. Immunological cross-reactivity and carbohydrate specificity indicate that jacalins possessing the new alpha-chain conserve structural and functional properties of the other members of Artocarpus genus.

Epitopic analysis of the Toxoplasma gondii major surface antigen SAG1

T and B cell epitopes of the major Toxoplasma gondii surface antigen SAG1 were studied following CNBr fragmentation. Three fragments, F1, F2 and F3, were obtained, of 19, 16.5 and 14 kDa, respectively. The positions of F1 F2 and F3 within the SAG1 protein were identified by N-terminal sequence determination. The F1 fragment located on residues 125-269 contains the C-terminus, and the fragment F2 (residues 1-124) is located at the N-terminal region. F3 is a C-terminal peptide about 40 amino acids shorter than the F1 fragment (residues 165-269). Polyclonal antibodies obtained from infected animals or humans and a monoclonal anti-SAG1 antibody did not recognize either the reduced protein or the reduced fragments on immunoblotting. The monoclonal antibody 1E5 did not recognize fragment F1. Mouse IgA and IgG antibodies from infected mouse sera and intestinal secretions, as well as human IgG antibodies, only recognized the whole protein and the F1 fragment. These results suggest that the fragment F1 encompasses all B cell epitopes recognized on the SAG1 protein after infection with the parasite and that the sequence 125-165 is essential for the structural integrity of these B cell epitopes. Murine anti-SAG1 T cell proliferation was observed in SAG1 immunized CBA/J mice (H-2k) and BALB/c mice (H-2d), but not in C57BL/6 mice (H-2b). The three fragments F1, F2 and F3 were able to induce specific proliferation of anti-SAG1 T cells from CBA/J mice, while only the F1 and F2 fragments induced specific blastogenesis of anti-SAG1 T cells from BALB/c mice.(ABSTRACT TRUNCATED AT 250 WORDS)

The alpha- and beta-subunits of the jacalins are cleavage products from a 17-kDa precursor

The jacalins of three Artocarpus species were purified by affinity chromatography on a desialylated mucin-CNBr-Sepharose 4B column. The beta-chains and the 14 kDa alpha-chains were separated by high pressure liquid chromatography and the 17 kDa chains by preparative electrophoresis. The 17 kDa and 14 kDa chains had a similar highly conserved N-terminal sequence. The beta-chains were different for the three species and Artocarpus champeden contained two different beta-chains. CNBr cleavage of the 17 kDa polypeptide of Artocarpus tonkinensis yielded one peptide more than the 14 kDa. The N-terminal sequence of this fragment was similar to that of the beta-chain proving that this chain results from a proteolytic cleavage at the C-terminus of the 17 kDa peptide. The large heterogeneity of the beta-chains of jacalins from different species could be used as a marker for evolutionary studies on the Artocarpus family.

Microheterogeneity of rat submaxillary gland kallikrein k10, a member of the kallikrein family

A tissue-kallikrein-related proteinase present in rat submaxillary glands, which was previously called endopeptidase k, has been further characterized and compared with other members of the kallikrein family. The partial primary structure of this proteinase, now called kallikrein k10, is very similar to that of proteinase B [Kato, H., Nakanishi, E., Enjyoji, K., Hayashi, I., Oh-Ishi, S. & Iwanaga, S. (1987) J. Biochem. (Tokyo) 102, 1389-1404] and T-kininogenase [Xiong, W., Chen. L. M. & Chao, J. (1990) J. Biol. Chem. 265, 2822-2827], but no corresponding gene or mRNA has so far been found. Kallikrein k10 is microheterogeneous due to variable glycosylation of its N-terminal light chain and to variable processing at its kallikrein loop, as shown by endo-beta-N-acetylglucosaminidase F treatment, amino acid sequence analysis and mass spectrometry. The enzymatic properties of the two molecular varieties of kallikrein k10 towards synthetic fluorogenic substrates are not significantly different. Both cleave specifically after Arg residues, but, in contrast to true tissue kallikrein, may accommodate either polar or nonpolar residues at position P2. Kallikrein k10 also differs from tissue kallikrein by its sensitivity to soyabean trypsin inhibitor. Its biological function may therefore differ from that of tissue kallikrein, especially as it does not induce a transient decrease in blood pressure when injected in vivo.

Substrate specificity of two kallikrein family gene products isolated from the rat submaxillary gland

Two proteinases which belong to the tissue kallikrein family were purified from rat submaxillary glands. These proteinases correspond to the products of the RSKG-7 and the rGK8 genes, as shown by the comparison of their partial amino-acid sequence with that deduced from nucleotide sequences. These two proteinases, kallikrein k7 and kallikrein k8, exhibit a marked preference for cleavage after arginyl residues. However, their overall specificities towards synthetic fluorogenic substrates differ significantly from each other and from that of true tissue kallikrein. Kallikrein k7 is strongly inhibited by soybean trypsin inhibitor, whereas kallikrein k8 is not. These data, demonstrating the individual specificity of these kallikrein-like proteinases, suggest that they could be involved in the processing of peptides other than kinins.

Time-Course Studies in Indole Alkaloid Accumulation and Changes in Tryptophan Decarboxylase and Strictosidine Synthase Activities: A Comparison in Three Strains of Catharanthus roseus Cells

Three different strains of CATHARANTHUS ROSEUS cells were compared during one subculture with regard to tryptophan, tryptamine, ajmalicine, serpentine contents and tryptophane decarboxylase (TDC) (4) and Strictosidine synthase activities. The strains differed greatly in their accumulation of tryptamine and alkaloid. The TDC of all three strains showed the highest activity during the growth phase and declined sharply at the end of this phase. On the contrary, strictosidine synthase activity was the lowest during the growth phase and increased distinctly at the same time when the alkaloids were accumulating. By comparing the three strains with each other, no correlation was observed between the values of enzymatic activities and the contents of accumulated alkaloids.

[Cytidine and deoxycytidine aminohydrolase activities from Zea mays L. aerial parts: probable existence of two isozymes both of which possess the two activities]

Enzymatic proteins with deoxycytidine and cytidine aminohydrolase activities were partially purified from Zea mays L. aerial parts by using ammonium sulfate fractionation, adsorption on calcium phosphate gel and chromatography on DEAE-cellulose.