Myeloid cell leukemia 1 (MCL-1), an anti-apoptotic BCL-2 family member active in the preservation of mitochondrial integrity during apoptosis, has fundamental roles in development and hematopoiesis and is dysregulated in human cancers. It bears a unique, intrinsically unstructured, N-terminal sequence, which leads to its instability in cells and hinders protein production and structural characterization. Here, we present collective data from NMR spectroscopy and titration calorimetry to reveal the selectivity of MCL-1 in binding BCL-2 homology 3 (BH3) ligands of interest for mammalian biology. The N-terminal sequence weakens the BH3 interactions but does not affect selectivity. Its removal by calpain-mediated limited proteolysis results in a stable BCL-2-like core domain of MCL-1 (cMCL-1). This core is necessary and sufficient for BH3 ligand binding. Significantly, we also characterized the in vitro protein-protein interaction between cMCL-1 and activated BID by size exclusion chromatography and NMR titrations. This interaction occurs in a very slow manner in solution but is otherwise similar to the interaction between cMCL-1 and BID-BH3 peptides. We also present the solution structure of complex cMCL-1⅐hBID-BH3, which completes the family portrait of MCL-1 complexes and may facilitate drug discovery against human tumors.The BCL-2 family of proteins plays a pivotal role in regulating apoptosis mainly by regulating the outer mitochondrial membrane integrity (1). They are classified into two functional groups: anti-apoptotic and pro-apoptotic. They each share conserved BH regions. The anti-apoptotics (BCL-2, BCL-w, BCL-X L , MCL-1, and A1) share up to four BH regions named BH1-4, 4 and prevent cells from entering apoptosis. The pro-apoptotics can be further grouped into the effectors and BH3-only proteins. The effectors, BAX and BAK, contain three BH (BH1-3) regions and promote cell death by oligomerization and mitochondria outer membrane permeabilization. The BH3-only proteins share the BH3 region of sequence similarity. Members of this group include BID, BIM, BAD, BMF, BIK, PUMA, Noxa, HRK/DPS (Harakiri), NIP3, bNIP3, and MULE. The BH3 region is 16 to 25 amino acid residues long and can promote apoptosis when introduced into cells. The three groups of BCL-2 proteins form a delicately balanced network of opposing functions that regulates the fate of the cell. MCL-1 belongs to the anti-apoptotic family but is unique due to its short half-life, the presence of an extra N-terminal sequence, and its particular selectivity in binding BH3 peptides. Its concentration in vivo is tightly regulated at multiple levels, and its N-terminal sequence presents many sites for post-translational modifications, including polyubiquitination (2, . These modifications are involved in regulating its activity in binding pro-apoptotic proteins, or in regulating its concentration by either promoting or blocking its degradation. A deregulated, high level of MCL-1 has been correlated with various hematopoietic and lymphoid cancers (8 -10)....
An extremely efficient bactericidal filter paper is developed that is capable of removing 99.99999% of Escherichia coli bacteria in a simple filtration process. The novel approach utilizes two active bactericidal components: a bactericidal agent, triclosan, which acts synergistically with a cationic polyelectrolyte binder with antibacterial properties. The biocide is incorporated into the block copolymer micelles attached to the cellulose fibers via the cationic polyelectrolyte. As the water containing the bacteria is passed by gravity through the filter paper, the bactericidal agents are transferred to the bacteria through collisions with the micelles or coated fibers. A synergy between the biocide and the polyelectrolyte is responsible for the extremely high efficiency in deactivating the bacteria. The filtered water is free of biocide other than that transported by the dead bacteria. This technology represents a very simple approach to provide potable water under a wide range of primitive conditions.
We previously produced a bactericidal filter paper loaded with PAA47-b-PS214 block copolymer micelles containing the biocide triclosan (TCN), using cationic polyacryamide (cPAM) as a binder. However, we encountered a very slow filtration, resulting in long bacteria deactivation times. Slow drainage occurred only when the filter paper was left to dry. It appears that the filter paper with cPAM and micelles develops hydrophobic properties responsible for this very slow filtration. Three approaches were taken to accelerate the very slow drainage all based on modification of binder-micelle interactions: (i) keeping the micelles wet, (ii) modification of the corona, and (iii) replacing cPAM with smaller and more highly charged cationic poly(isopropanol dimethylammonium) chloride (PIDMAC). In all cases, the drainage time of bactericidal filter paper became close to that of untreated filter paper, without decreasing its efficiency. Moreover, replacing cPAM with PIDMAC led to a much more efficient bactericidal filter paper that reduced bacteria viability by more than 6 orders of magnitude. In addition to resolving the hydrophobic drainage hurdle, the three solutions also offer a better understanding of the interaction between cPAM and micelles in the filter paper.
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