Duplication of a Single Strand in a β‑Sheet Can Produce a New Switching Function in a Photosensory Protein

Duplication of a single β-strand that forms part of a β-sheet in photoactive yellow protein (PYP) was found to produce two approximately isoenergetic protein conformations, in which either the first or the second copy of the duplicated β-strand participates in the β-sheet. Whereas one conformation (big-loop) is more stable at equilibrium in the dark, the other conformation (long-tail) is populated after recovery from blue light irradiation. By appending a recognition motif (E-helix) to the C-terminus of the protein, we show that β-strand duplication, and the resulting possibility of β-strand slippage, can lead to a new switchable protein–protein interaction. We suggest that β-strand duplication may be a general means of introducing two-state switching activity into protein structures

Hydrothermal Synthesis of Open-Framework Borophosphates with Tunable Micropore Sizes, Crystal Morphologies, and Thermal Stabilities

Thermal stabilities of zeolitic frameworks are important parameters for many applications. Two decades of research have produced only a very small number of zeolitic borophosphates such as Na₂[VO­(B₂O)­(PO₄)₂(HBO₃)]·<i>x</i>H₂O (<i>x</i> <b> ≈ </b> 2.92) (denoted as <b>B</b>_<b>3</b><b>P</b>_<b>2</b>), which shows the onset dehydration and a complete decomposition at 200 and 400 °C, respectively. In order to enhance thermal stabilities of borophosphate frameworks, a water-deficient hydrothermal route with phosphoric acid as the sole solvent has been developed and led to controlled syntheses of <b>B</b>_<b>3</b><b>P</b>_<b>2</b> and a new vanadium borophosphate, K_1.33Na_0.67[VO­(B₂O)­(PO₄)₂(HPO₄)]·<i>x</i>H₂O (<i>x</i> <b> ≈ </b> 1.63) (denoted as <b>B</b>_<b>2</b><b>P</b>_<b>3</b>). The latter is the first-ever borophosphate possessing the zeolite RHO-type net and is characterized by superlarge spherical cages, including 16-ring and 8-ring channels along the axes and 12-ring channels along the diagonals of the cubic cell. The new compound <b>B</b>_<b>2</b><b>P</b>_<b>3</b> has larger structural cages and higher thermal stability than <b>B</b>_<b>3</b><b>P</b>_<b>2</b>, where the enhanced thermal stability is attributable to different bonding arising from the substitution of [BO₂(OH)] by [PO₃(OH)] in the framework. This is the first demonstration that the micropore size, crystal morphology, and thermal stability of zeolitic borophosphates can be tuned by changing the fundamental building units of their frameworks via adjusting the B/P ratios in the starting materials