Showing papers on "Pore forming protein published in 1987"

Dissociation of membrane binding and lytic activities of the lymphocyte pore-forming protein (perforin).

Abstract: Granules isolated from CTL and NK cells contain a cytolytic pore-forming protein (PFP/perforin). At low temperatures (on ice), PFP binds to erythrocyte membranes without producing hemolysis. Hemolysis occurs when the PFP-bound erythrocytes are warmed up to 37 degrees C, which defines a temperature-dependent, lytic (pore-formation) step distinct from the membrane-binding event. Ca2+ and neutral pH are required for both membrane binding and pore formation by PFP. Serum, LDL, HDL, and heparin inhibit the hemolytic activity of PFP by blocking its binding to lipid membranes. Lysis by PFP that has bound to erythrocyte membranes is no longer susceptible to the effect of these inhibitors. The hemolytic activities associated with intact granules and solubilized PFP show different requirements for Ca2+ and pH, indicating that cytolysis produced by isolated granules may involve an additional step, possibly fusion of granules with membranes. It is suggested that three distinct Ca2+- and pH-dependent events may be involved during cell killing by CTL and NK cells: fusion of cytoplasmic granules of effector cells with their plasma membrane, releasing PFP from cells; binding of the released PFP to target membranes; and insertion of monomers and the subsequent formation of lytic pores in the target membrane. The serum-mediated inhibition of membrane binding by PFP could prevent the accidental injury of bystander cells by cell-released PFP, but would allow cytolysis to proceed to completion once PFP has bound to the target membrane.

Localization of a pore-forming protein (perforin) in granulated metrial gland cells.

Abstract: Several studies have suggested that the granulated metrial gland (GMG) cells of the metrial gland (MG) may be natural killer (NK)-like cells. The cytotoxicity of NK cells involves secretion of a pore-forming protein termed perforin, which can polymerize on the target cell membrane to form transmembrane pores that are thought to be involved in target cell death. In the present study, we used an antiserum against perforin to determine whether this protein can be detected immunohistochemically in GMG cells. Mouse uteri were fixed by vascular perfusion with several fixatives on Day 14 of pregnancy, and tissue sections were labeled by an indirect immunofluorescence method. Specific perforin labeling was detected in GMG cells throughout the MG, in the decidua basalis, and in the labyrinthine placenta. The presence of perforin in GMG cells supports the suggestion that they may be NK-like cells.

A comparative study on the phoE genes of three enterobacterial species. Implications for structure-function relationships in a pore-forming protein of the outer membrane.

Abstract: The cloned phoE genes from Enterobacter cloacae and Klebsiella pneumoniae are normally expressed and regulated in Escherichia coli K-12, and their products are correctly assembled into the outer membrane. Differences between the three PhoE proteins were found with binding of two out of ten monoclonal antibodies directed against the cell-surface-exposed part and in pore characteristics, but not in phage receptor function. The DNA sequences of the E. cloacae and K. pneumoniae phoE genes were determined and used to predict the primary structures of the encoded proteins. In the upstream non-coding regions, which showed more variations among the three genes than the coding regions, conserved sequences were identified which might be involved in regulation of phoE gene expression. Comparison of the predicted PhoE primary structures revealed a high degree of homology, with 81% of the amino acid residues being identical in all three proteins. Four small variable regions were found where differences are the most pronounced, corresponding to regions which were previously predicted to be exposed at the cell surface. Implications of the sequence comparison for structure-function relationships in PhoE protein are discussed.

Physiological Function and Physical Characteristics of the Chloroplast Phosphate Translocator

Abstract: The chloroplast envelope has two distinct membranes: an inner and an outer membrane. The outer membrane is unspecifically permeable for substances with molecular weights up to 10 kD. This is due to the presence of a pore forming protein, named chloroplast porin, with a pore diameter of 2.5–3.0 nm which is the largest diameter of all porins pores known so far (1). The inner envelope membrane is the functional barrier between the chloroplasts and the cytosol. It is the site of numerous metabolite translocators which, apparently, are involved in coordinating the metabolism in the stromal and the cytosolic compartment.