Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.52 (PNGase F)
 1,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Factor B is a glycoprotein which plays an essential role in the alternative pathway of complement activation. It carries the proteolytic activity of the convertases, and its physiological breakdown products Ba and Bb have some effects on the cells of the immune system. Human factor B exhibits a microheterogeneity and five isoforms are present in serum. The nature and origin of the microheterogeneity was investigated by using electrophoretic techniques. Treatments of factor B with neuraminidase and glycopeptidase F show that this microheterogeneity is mainly due to differences in its sialic acid content, varying from seven to eleven residues per molecule, and resulting in different oligosaccharide structures. However, deglycosylated factor B reveals a residual, nonallotypic variation in the Bb region of the polypeptide backbone. We confirm the presence of four asparagine-linked oligosaccharide chains of the complex type in native factor B, two of which are located in the Ba fragment, and the two others in the Bb fragment. The prevalent isoform of the native protein carries two sialic acid residues per oligosaccharide chain. Biosynthesis experiments show that the microheterogeneity of secreted factor B from HepG2 cells is acquired during the processing of its glycans. However, in vitro-secreted factor B is more heterogeneous than the serum protein. We propose a structural model for the microheterogeneity of the native protein and its physiological fragments. We discuss as well the feasibility of electrophoretic techniques to deal with microheterogeneity analysis.
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PMID:Heterogeneous nature of human complement factor B: an electrophoretic approach for the analysis of its oligosaccharide chain structure and its physiological breakdown products. 277 35

Epimastigotes (EPI) of Trypanosoma cruzi are highly sensitive to lysis in fresh normal human serum by the alternative complement pathway (ACP). In contrast, metacyclic trypomastigotes (CMT) derived from EPI in stationary culture fail to activate the ACP and are thus resistant to serum-mediated lysis. To investigate the nature of the parasitic surface molecules which enable infective metacyclic trypomastigotes to evade the ACP, CMT were treated with a variety of different proteolytic and glycosidic enzymes, and their sensitivity to ACP-dependent lysis was tested. Pretreatment with pronase was found to cause a near complete reversal in the resistance of CMT to serum lysis, whereas trypsin or chymotrypsin induced smaller increases in complement sensitivity. Similarly, pretreatment with N-glycanase or neuraminidase also partially abrogated the resistance of CMT to ACP-dependent lysis. The effect of these enzymes on susceptibility to complement-mediated lysis was paralleled in increased C3 and C9 deposition on the organism. In addition, electrophoretic analysis of parasite-bound C3 indicated that the hemolytically inactive fragment, iC3b, was the major form of the molecule on CMT, while the hemolytically active fragment, C3b, predominated on pronase-treated CMT. Furthermore, when C3 was deposited on the parasite surface by means of purified ACP components, 80% of C3b on pronase-pretreated CMT but only 14% of the C3b on CMT bound the amplification protein factor B with high affinity, a prerequisite for efficient ACP activation. When cultured at 37 degrees C after pronase treatment, CMT gradually regained their resistance to ACP-mediated lysis. This process was blocked if puromycin, cycloheximide, or tunicamycin were included in the culture medium. The above findings suggest that evasion of the ACP by CMT is dependent on the developmentally regulated synthesis of protein as well as N-linked carbohydrate chains. A stage-specific 90,000 to 115,000 m.w. glycoprotein doublet present on the surface of CMT was shown to be uniquely sensitive to pronase digestion. Thus, this complex, which is also recognized by a CMT-specific monoclonal antibody, may be the glycoprotein component responsible for control of ACP activation
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PMID:Evasion of the alternative complement pathway by metacyclic trypomastigotes of Trypanosoma cruzi: dependence on the developmentally regulated synthesis of surface protein and N-linked carbohydrate. 353 42