Phytochrome photoreceptors mediate light responses in plants and in many microorganisms. Here we report studies using ¹ H– ¹³ C magic-angle spinning NMR spectroscopy of the sensor module of cyanobacterial phytochrome Cph1. Two isoforms of the red-light absorbing Pr ground state are identified. Conclusive evidence that photoisomerization occurs at the C15-methine bridge leading to a β -facial disposition of the ring D is presented. In the far-red-light absorbing Pfr state, strong hydrogen-bonding interactions of the D -ring carbonyl group to Tyr-263 and of N24 to Asp-207 hold the chromophore in a tensed conformation. Signaling is triggered when Asp-207 is released from its salt bridge to Arg-472, probably inducing conformational changes in the tongue region. A second signal route is initiated by partner swapping of the B -ring propionate between Arg-254 and Arg-222.

Since the solution of the molecular structures of members of the voltage dependent anion channels (VDACs), the N-terminal α-helix has been the main focus of attention, since its strategic location, in combination with its putative conformational flexibility, could define or control the channel’s gating characteristics. Through engineering of two double-cysteine mVDAC1 variants we achieved fixing of the N-terminal segment at the bottom and midpoint of the pore. Whilst cross-linking at the midpoint resulted in the channel remaining constitutively open, cross-linking at the base resulted in an “asymmetric” gating behavior, with closure only at one electric field´s orientation depending on the channel’s orientation in the lipid bilayer. Additionally, and while the native channel adopts several well-defined closed states (S1 and S2), the cross-linked variants showed upon closure a clear preference for the S2 state. With native-channel characteristics restored following reduction of the cysteines, it is evident that the conformational flexibility of the N-terminal segment plays indeed a major part in the control of the channel’s gating behavior.

Phytochrome photoreceptors in plants and microorganisms switch photochromically between two states, controlling numerous important biological processes. Although this phototransformation is generally considered to involve rotation of ring D of the tetrapyrrole chromophore, Ulijasz et al. (Ulijasz, A. T., Cornilescu, G., Cornilescu, C. C., Zhang, J., Rivera, M., Markley, J. L., and Vierstra, R. D. (2010) Nature 463, 250–254) proposed that the A-ring rotates instead. Here, we apply magic angle spinning NMR to the two parent states following studies of the 23-kDa GAF (cGMP phosphodiesterase/adenylyl cyclase/FhlA) domain fragment of phytochrome from Synechococcus OS-B′. Major changes occur at the A-ring covalent linkage to the protein as well as at the protein residue contact of ring D. Conserved contacts associated with the A-ring nitrogen rule out an A-ring photoflip, whereas loss of contact of the D-ring nitrogen to the protein implies movement of ring D. Although none of the methine bridges showed a chemical shift change comparable with those characteristic of the D-ring photoflip in canonical phytochromes, denaturation experiments showed conclusively that the same occurs in Synechococcus OS-B′ phytochrome upon photoconversion. The results are consistent with the D-ring being strongly tilted in both states and the C15=C16 double bond undergoing a Z/E isomerization upon light absorption. More subtle changes are associated with the A-ring linkage to the protein. Our findings thus disprove A-ring rotation and are discussed in relation to the position of the D-ring, photoisomerization, and photochromicity in the phytochrome family.

Voltage dependent anion channels (VDACs) are the most abundant proteins in the outer mitochondrial membrane. Although they are essential in metabolite exchange, cell defense and apoptosis, the molecular mechanism of these VDAC-mediated processes remains elusive. Here we review recent progress in terms of VDACs’ structure and regulation, with a special focus on the molecular aspects of gating and the interaction with effector proteins.

Summary: Helicobacter pyloriis a Gram‐negative pathogenic microaerophile with a particular tropism for the mucosal surface of the gastric epithelium. Despite its obligatory microaerophilic character, it can metabolized‐glucose and/ord‐galactose in both oxidative and fermentative pathways via a Na⁺‐dependent secondary active transport, a glucokinase and enzymes of the pentose phosphate pathway. We have assigned the Na⁺‐dependent transport of glucose to the protein product of theH. pylori 1174gene. The gene was heterologously expressed in a glucose transport‐deficientEscherichia colistrain, where transport activities of radiolabelledd‐glucose,d‐galactose and 2‐deoxy‐d‐glucose were restored, consistent with the expected specificity of the hexose uptake system inH. pylori.d‐Mannose was also identified as a substrate. The HP1174 transport protein was purified and reconstituted into proteoliposomes, where sodium dependence of sugar transport activity was demonstrated. Additionally the tryptophan/tyrosine fluorescence of the purified protein showed quenching by 2‐deoxy‐d‐glucose,d‐mannose,d‐glucose ord‐galactose in the presence of sodium ions. This is the first reported purification and characterization of an active glucose transport protein member of the TC 2.1.7 subgroup of the Major Facilitator Superfamily, constituting the route for entry of sugar nutrients intoH. pylori. A model is derived of its three‐dimensional structure as a paradigm of the family.