Showing papers on "Pore forming protein published in 2000"

Bcl-2 and Bax regulate the channel activity of the mitochondrial adenine nucleotide translocator.

Abstract: Bcl-2 family protein including anti-apoptotic (Bcl-2) or pro-apoptotic (Bax) members can form ion channels when incorporated into synthetic lipid bilayers. This contrasts with the observation that Bcl-2 stabilizes the mitochondrial membrane barrier function and inhibits the permeability transition pore complex (PTPC). Here we provide experimental data which may explain this apparent paradox. Bax and adenine nucleotide translocator (ANT), the most abundant inner mitochondrial membrane protein, can interact in artificial lipid bilayers to yield an efficient composite channel whose electrophysiological properties differ quantitatively and qualitatively from the channels formed by Bax or ANT alone. The formation of this composite channel can be observed in conditions in which Bax protein alone has no detectable channel activity. Cooperative channel formation by Bax and ANT is stimulated by the ANT ligand atractyloside (Atr) but inhibited by ATP, indicating that it depends on the conformation of ANT. In contrast to the combination of Bax and ANT, ANT does not form active channels when incorporated into membranes with Bcl-2. Rather, ANT and Bcl-2 exhibit mutual inhibition of channel formation. Bcl-2 prevents channel formation by Atr-treated ANT and neutralizes the cooperation between Bax and ANT. Our data are compatible with a menage a trois model of mitochondrial apoptosis regulation in which ANT, the likely pore forming protein within the PTPC, interacts with Bax or Bcl-2 which influence its pore forming potential in opposing manners.

Cyclic Peptides as Molecular Adapters for a Pore-Forming Protein

Abstract: Recently, cyclodextrins were shown to act as adapters for the pore-forming protein staphylococcal α-hemolysin (αHL). The bagel-shaped molecules bind in the lumen of the transmembrane channel formed...

Structure-function studies of tryptophan mutants of equinatoxin II, a sea anemone pore-forming protein

Abstract: Equinatoxin II (EqtII) is a eukaryotic cytolytic toxin that avidly creates pores in natural and model lipid membranes. It contains five tryptophan residues in three different regions of the molecule. In order to study its interaction with the lipid membranes, three tryptophan mutants, EqtII Trp(45), EqtII Trp(116/117) and EqtII Trp(149), were prepared in an Escherichia coli expression system [here, the tryptophan mutants are classified according to the position of the remaining tryptophan residue(s) in each mutated protein]. They all possess a single intrinsic fluorescent centre. All mutants were less haemolytically active than the wild-type, although the mechanism of erythrocyte damage was the same. EqtII Trp(116/117) resembles the wild-type in terms of its secondary structure content, as determined from Fourier-transform infrared (FTIR) spectra and its fluorescent properties. Tryptophans at these two positions are buried within the hydrophobic interior of the protein, and are transferred to the lipid phase during the interaction with the lipid membrane. The secondary structure of the other two mutants, EqtII Trp(45) and EqtII Trp(149), was altered to a certain extent. EqtII Trp(149) was the most dissimilar from the wild-type, displaying a higher content of random-coil structure. It also retained the lowest number of nitrogen-bound protons after exchange with (2)H(2)O, which might indicate a reduced compactness of the molecule. Tryptophans in EqtII Trp(45) and EqtII Trp(149) were more exposed to water, and also remained as such in the membrane-bound form.

Molecular Mechanisms of Immune Dysfunction in Renal Cell Carcinoma

Abstract: The development of an effective host immune response against neoplastic cells requires activation of T cells following recognition of tumor-associated antigens expressed on the appropriate antigen presenting cells (1). The generation of a cell-mediated cellular response typically involves CD8+ T cells that recognize peptides presented by MHC class I whereas CD4+ T cells recognize peptides presented by major histocompatibility complex (MHC) class II along with the appropriate costimulatory molecules (B7.1 and B7.2). Activation of the Th1 CD4+ cells leads to the production of cytokines such as interleukin-2 (IL-2) that provides a critical signal for clonal expansion of antigen activated lymphocytes. IL-2 signaling also upregulates expression of effector molecules (granzyme B and pore forming protein) requisite for the cytolytic function of CD8+ T cells. Another critical cytokine is gamma-interferon (IFNγ), produced by both Th1 CD4+ and a subset of CD8+ T cells, that further promotes the development of a cellular response by enhancing MHC and costimulatory molecule expression as well as by activating macrophages. Activation of T-cell immunity is dependent on normal intracellular signaling through the T-cell receptor and subsequent downstream induction of a variety of transcriptional factors that regulate gene expression of cytokines, chemokines, and receptors involved in T-cell responses (1, 2).