Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.64 (proteinase K)
 4,071 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It is well known that lipopolysaccharide (LPS) of Gram-negative bacteria triggers antibacterial responses to mammalian macrophages [Weinstein, S., Gold, M. R. & DeFranco, A. (1991) Proc. Natl Acad. Sci. USA 88, 4148-4152] and insect hemocytes [Charalambidis, N.D., Zervas, C.G., Lambropoulou, M., Katsoris, P.G. & Marmaras, V.J. (1995) Eur J. Cell Biol. 67, 32-41], via protein-tyrosine phosphorylation. In this study we show that insect hemocytes in response to LPS facilitate internalization of LPS (either cell-associated or cell-free). According to our data, the recognition and covalent association of LPS (either cell-associated or cell-free) to the hemocyte surface are essential initial steps for LPS internalization. LPS (Escherichia coli) recognizes membrane effector 47-kDa protein (p47) and then crosslinks to membrane-associated p47 (mp47) via the intermediacy of tyrosine derivatives generated by the action of phenol oxidase, as is the case for cuticular protein-chitin crosslinks during sclerotization [Shaefer, J., Kramer, K.J., Garbow, J.R., Jacob, G.S., Stejskal, E.O., Hopkins, T.L. & Speirs, R.D. (1987) Science 235, 1200-1204]. The covalent association of LPS to the hemocyte surface appears to be a prerequisite for LPS internalization as judged by the resistance of LPS binding to dissociation by proteinase K. In addition, our results show that the effector molecules participating in LPS covalent association at the cell surface and LPS internalization are not involved in LPS-induced activation of hemocytes. However, the fact that genistein, as well as the inhibitors of LPS-dependent secretion, block LPS covalent association at the cell surface and LPS internalization provides a preliminary characterization of an LPS signal-transduction-dependent process which is apparently involved.
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PMID:Covalent association of lipopolysaccharide at the hemocyte surface of insects is an initial step for its internalization--Protein-tyrosine phosphorylation requirement. 861 65

Bacterial lipopolysaccharide (LPS) attachment at the hemocyte surface is based on the crosslinking of surface associated p47 to LPS, via the intermediacy of tyrosine derivatives generated by the action of phenoloxidase (PO). This attachment is an initial step for LPS internalization from hemocytes (Charalambidis et al., 1996). The results presented clearly show the critical role of hemocyte associated PO activity in the above processes. Biochemical and immunofluorescent analysis demonstrated unambiguously the presence of prophenoloxidase (proPO) on the hemocyte surface. The cell-surface expression of proPO appeared to be LPS-independent, whereas its activation was LPS-dependent. The activation of cell surface proPO involves a limited proteolysis, since upon activation with chymotrypsin proPO is converted to a set of smaller molecular weight proteins with PO activity. The activation appears to be due to enzyme activators, serine proteases, released upon LPS-stimulation. This hypothesis was supported from the activation of membrane proPO by the culture medium of hemocytes which have been triggered with LPS. In addition, proPO, activation was abolished by inhibitors of secretion and PMSF. The release of proPO activators upon LPS-stimulation is mediated via protein tyrosine phosphorylation, as genistein inhibited proPO activation, a situation similar to that reported by us for the release of the effector protein p47 (Charalambidis et al., 1995). The LPS-stimulated activation of cell-surface proPO is a prerequisite for LPS (either cell associated or cell free) internalization, as judged by the resistance of LPS binding to dissociation by proteinase K.
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PMID:Hemocyte surface phenoloxidase (PO) and immune response to lipopolysaccharide (LPS) in Ceratitis capitata. 901 31