Background: Evolutionary conserved Bax inhibitor-1 (BI-1) protects against ER stress-mediated apoptosis. Results: We identified a Ca 2ϩ -permeable channel pore in the C terminus of BI-1. Critical pore properties are an ␣-helical structure and two aspartate residues conserved among animals, but not among plants and yeast. Conclusion: C-terminal domain of BI-1 harbors a Ca 2ϩ -permeable channel pore. Significance: BI-1 has Ca 2ϩ channel properties likely relevant for its function in ER stress and apoptosis. Bax inhibitor-1 (BI-1) is a multitransmembrane domainspanning endoplasmic reticulum (ER)-located protein that is evolutionarily conserved and protects against apoptosis and ER stress. Furthermore, BI-1 is proposed to modulate ER Ca 2؉homeostasis by acting as a Ca 2؉ -leak channel. Based on experimental determination of the BI-1 topology, we propose that its C terminus forms a Ca 2؉ pore responsible for its Ca 2؉ -leak properties. We utilized a set of C-terminal peptides to screen for Ca 2؉ leak activity in unidirectional 45 Ca 2؉ -flux experiments and identified an ␣-helical 20-amino acid peptide causing Ca 2؉ leak from the ER. The Ca 2؉ leak was independent of endogenous ER Ca 2؉ -release channels or other Ca 2؉ -leak mechanisms, namely translocons and presenilins. The Ca 2؉ -permeating property of the peptide was confirmed in lipid-bilayer experiments. Using mutant peptides, we identified critical residues responsible for the Ca 2؉ -leak properties of this BI-1 peptide, including a series of critical negatively charged aspartate residues. Using peptides corresponding to the equivalent BI-1 domain from various organisms, we found that the Ca 2؉ -leak properties were conserved among animal, but not plant and yeast orthologs. By mutating one of the critical aspartate residues in the proposed Ca 2؉ -channel pore in full-length BI-1, we found that Asp-213 was essential for BI-1-dependent ER Ca 2؉ leak. Thus, we elucidated residues critically important for BI-1-mediated Ca 2؉ leak and its potential channel pore. Remarkably, one of these residues was not conserved among plant and yeast BI-1 orthologs, indicating that the ER Ca2؉ -leak properties of BI-1 are an added function during evolution. leak from the ER (9, 10). BI-1 seems to be strongly evolutionarily conserved and BI-1 orthologs from plants can substitute for mammalian BI-1 in regard to its anti-apoptotic function (11). Besides this, other diverse functions of BI-1 have been described. BI-1 is a negative regulator of the ER-stress sensor (12), it interacts with G-actin and increases actin polymerization (13), enhances cancer metastasis by altering glucose metabolism and by activating a sodium-hydrogen exchanger (14), and it reduces production of reactive oxygen species through direct interaction with NADPH-P450 reductase (15), a member of the microsomal monooxygenase system.Recently, the role of BI-1 in Ca 2ϩ signaling has been further explored. The effect of BI-1 on cell death seems to involve changes in the amount of Ca 2ϩ that is releasable from intrace...

The zeamines (zeamine, zeamine I, and zeamine II) constitute an unusual class of cationic polyamine-polyketide-nonribosomal peptide antibiotics produced by Serratia plymuthica RVH1. They exhibit potent bactericidal activity, killing a broad range of Gram-negative and Gram-positive bacteria, including multidrug-resistant pathogens. Examination of their specific mode of action and molecular target revealed that the zeamines affect the integrity of cell membranes. The zeamines provoke rapid release of carboxyfluorescein from unilamellar vesicles with different phospholipid compositions, demonstrating that they can interact directly with the lipid bilayer in the absence of a specific target. DNA, RNA, fatty acid, and protein biosynthetic processes ceased simultaneously at subinhibitory levels of the antibiotics, presumably as a direct consequence of membrane disruption. The zeamine antibiotics also facilitated the uptake of small molecules, such as 1-N-phenylnaphtylamine, indicating their ability to permeabilize the Gram-negative outer membrane (OM). The valine-linked polyketide moiety present in zeamine and zeamine I was found to increase the efficiency of this process. In contrast, translocation of the large hydrophilic fluorescent peptidoglycan binding protein PBD KZ -GFP was not facilitated, suggesting that the zeamines cause subtle perturbation of the OM rather than drastic alterations or defined pore formation. At zeamine concentrations above those required for growth inhibition, membrane lysis occurred as indicated by time-lapse microscopy. Together, these findings show that the bactericidal activity of the zeamines derives from generalized membrane permeabilization, which likely is initiated by electrostatic interactions with negatively charged membrane components.

The synthesis and characterization of a novel gadolinium(III) DOTA complex functionalized with a boron-dipyrromethene derivative (BODIPY) is described. The assembly of the complex relies on azide diazotransfer chemistry in a copper tube flow reactor. The azide thus formed is coupled directly with an alkyne via click chemistry, resulting into a paramagnetic and luminescent gadolinium(III) complex. Luminescent data and relaxometric properties of the complex have been evaluated, suggesting the potential applicability of the complexes as a bimodal contrast agent for magnetic resonance and optical imaging. The complex displays a bright emission at 523 nm with an absorption maximum of 507 nm and high quantum yields of up to 83% in water. The proton relaxivity of the complex measured at 310 K and at frequencies of 20 and 60 MHz had the values of 3.9 and 3.6 s −1 •mM −1 , respectively.

The anti-apoptotic Bcl-2 protein is the founding member and namesake of the Bcl-2-protein family. It has recently been demonstrated that Bcl-2, apart from its anti-apoptotic role at mitochondrial membranes, can also directly interact with the inositol 1,4,5-trisphosphate receptor (IP3R), the primary Ca2+-release channel in the endoplasmic reticulum (ER). Bcl-2 can thereby reduce pro-apoptotic IP3R-mediated Ca2+ release from the ER. Moreover, the Bcl-2 homology domain 4 (Bcl-2-BH4) has been identified as essential and sufficient for this IP3R-mediated anti-apoptotic activity. In the present study, we investigated whether the reported inhibitory effect of a Bcl-2-BH4 peptide on the IP 3R1 was related to the distinctive α-helical conformation of the BH4 domain peptide. We therefore designed a peptide with two glycine “hinges” replacing residues I14 and V15, of the wild-type Bcl-2-BH4 domain (Bcl-2-BH4-IV/GG). By comparing the structural and functional properties of the Bcl-2-BH4-IV/GG peptide with its native counterpart, we found that the variant contained reduced α-helicity, neither bound nor inhibited the IP 3R1 channel, and in turn lost its anti-apoptotic effect. Similar results were obtained with other substitutions in Bcl-2-BH4 that destabilized the α-helix with concomitant loss of IP3R inhibition. These results provide new insights for the further development of Bcl-2-BH4-derived peptides as specific inhibitors of the IP3R with significant pharmacological implications.

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