Metal-organic supercontainers (MOSCs) represent a new family of synthetic receptors derived from container precursors and featuring both endo and exo cavities. A neutral MOSC has been functionalized into an anionic container by incorporating sulfo groups. The anionic MOSC exhibits cavity-specific binding properties in both solid state and solution.
Human acetyltransferases MOZ and MORF are implicated in chromosomal translocations associated with aggressive leukemias. Oncogenic translocations involve the far amino terminus of MOZ/MORF, the function of which remains unclear. Here, we identified and characterized two structured winged helix (WH) domains, WH1 and WH2, in MORF and MOZ. WHs bind DNA in a cooperative manner, with WH1 specifically recognizing unmethylated CpG sequences. Structural and genomic analyses show that the DNA binding function of WHs targets MORF/MOZ to gene promoters, stimulating transcription and H3K23 acetylation, and WH1 recruits oncogenic fusions to HOXA genes that trigger leukemogenesis. Cryo-EM, NMR, mass spectrometry and mutagenesis studies provide mechanistic insight into the DNA-binding mechanism, which includes the association of WH1 with the CpG-containing linker DNA and binding of WH2 to the dyad of the nucleosome. The discovery of WHs in MORF and MOZ and their DNA binding functions could open an avenue in developing therapeutics to treat diseases associated with aberrant MOZ/MORF acetyltransferase activities.
Cardiolipin (CL), an anionic phospholipid constituting 20% of the inner mitochondrial membrane (IMM) of eukaryotes, stabilizes electron transport chain (ETC) complexes and is a signaling agent in the early stages of apoptosis. For apoptosis, CL moves from the inner to the outer leaflet of the IMM via a poorly understood mechanism. Relative to cylindrically shaped lipids like dioleoylphosphatidylcholine (DOPC) and dioleoylphosphatidylglycerol (DOPG), cone-shaped CL should prefer the concave surfaces of lipid bilayers. Using the fluorophore, 1,1,2,2-tetrakis[4-(2trimethylammonioethoxy)phenyl]ethene, we have measured CL versus DOPG partitioning to the inner versus the outer leaflet of liposomes in mixed lipid systems with DOPC. DOPG shows no leaflet preference. However, CL has a 4:1 preference for the concave surface of the inner leaflet of liposomes. To further test the inner leaflet preference of CL, we show that cytochrome c binding to the outer convex surface of 20% CL/80% DOPC vesicles is strongly attenuated. Because the outer leaflet of intracristal regions of the IMM has a concave curvature, the preference of CL for concave surfaces may facilitate the transport of CL from the inner to the outer leaflet of the IMM needed for CL remodeling, the optimal functioning of the ETC, and signaling in the early stages of apoptosis.
The
structure of the first ubiquitin-associated domain from HHR23A,
UBA(1), was determined by X-ray crystallography at a 1.60 Å resolution,
and its stability, folding kinetics, and residual structure under
denaturing conditions have been investigated. The concentration dependence
of thermal denaturation and size-exclusion chromatography indicate
that UBA(1) is monomeric. Guanidine hydrochloride (GdnHCl) denaturation
experiments reveal that the unfolding free energy, ΔG
u°′(H2O), of UBA(1) is
2.4 kcal mol–1. Stopped-flow folding kinetics indicates
sub-millisecond folding with only proline isomerization phases detectable
at 25 °C. The full folding kinetics are observable at 4 °C,
yielding a folding rate constant, k
f,
in the absence of a denaturant of 13,000 s–1 and
a Tanford β-value of 0.80, consistent with a compact transition
state. Evaluation of the secondary structure via circular dichroism
shows that the residual helical structure in the denatured state is
replaced by polyproline II structure as the GdnHCl concentration
increases. Analysis of NMR secondary chemical shifts for backbone 15NH, 13CO, and 13Cα atoms between
4 and 7 M GdnHCl shows three islands of residual helical secondary
structure that align in sequence with the three native-state helices.
Extrapolation of the NMR data to 0 M GdnHCl demonstrates that helical
structure would populate to 17–33% in the denatured state under
folding conditions. Comparison with NMR data for a peptide corresponding
to helix 1 indicates that this helix is stabilized by transient tertiary
interactions in the denatured state of UBA(1). The high helical content
in the denatured state, which is enhanced by transient tertiary interactions,
suggests a diffusion–collision folding mechanism.
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