Discotic Star Mesogen with Thymine Nucleobases Exhibiting a Rare Gyroid Cubic Mesophase with 3D Conductivity.

A unique gyroid cubic phase has been discovered for a discotic star mesogen with three covalently attached DNA bases. In this cubic I a 3 ‾ d ${Ia\bar{3}d}$ phase, the conjugated core of the mesogens and the thymine pseudo guests self-assemble in mirror image continuous networks, representing a semiconducting material with three-dimensional transport pathways. The hole carrier mobilities are found to be in the typical range of poly(phenylenevinylene) scaffolds. This structure is stabilized by a weak hydrogen bonding between the thymine bases and can be switched to a columnar liquid crystal - thermally and by the addition of complementary adenine guests.

Central role of Tim17 in mitochondrial presequence protein translocation.

The presequence translocase of the mitochondrial inner membrane (TIM23) represents the major route for the import of nuclear-encoded proteins into mitochondria1,2. About 60% of more than 1,000 different mitochondrial proteins are synthesized with amino-terminal targeting signals, termed presequences, which form positively charged amphiphilic α-helices3,4. TIM23 sorts the presequence proteins into the inner membrane or matrix. Various views, including regulatory and coupling functions, have been reported on the essential TIM23 subunit Tim17 (refs. 5-7). Here we mapped the interaction of Tim17 with matrix-targeted and inner membrane-sorted preproteins during translocation in the native membrane environment. We show that Tim17 contains conserved negative charges close to the intermembrane space side of the bilayer, which are essential to initiate presequence protein translocation along a distinct transmembrane cavity of Tim17 for both classes of preproteins. The amphiphilic character of mitochondrial presequences directly matches this Tim17-dependent translocation mechanism. This mechanism permits direct lateral release of transmembrane segments of inner membrane-sorted precursors into the inner membrane.