Cation Diffusion Facilitators Transport Initiation and Regulation Is Mediated by Cation Induced Conformational Changes of the Cytoplasmic Domain

Cation diffusion facilitators (CDF) are part of a highly conserved protein family that maintains cellular divalent cation homeostasis in all domains of life. CDF's were shown to be involved in several human diseases, such as Type-II diabetes and neurodegenerative diseases. In this work, we employed a multi-disciplinary approach to study the activation mechanism of the CDF protein family. For this we used MamM, one of the main ion transporters of magnetosomes - bacterial organelles that enable magnetotactic bacteria to orientate along geomagnetic fields. Our results reveal that the cytosolic domain of MamM forms a stable dimer that undergoes distinct conformational changes upon divalent cation binding. MamM conformational change is associated with three metal binding sites that were identified and characterized. Altogether, our results provide a novel auto-regulation mode of action model in which the cytosolic domain's conformational changes upon ligand binding allows the priming of the CDF into its transport mode

Biogenic guanine crystals are solid solutions of guanine and other purine metabolites

Highly reflective crystals of the nucleotide base guanine are widely distributed in animal coloration and visual systems. Organisms precisely control the morphology and organization of the crystals to optimize different optical effects, but little is known about how this is achieved. Here we examine a fundamental question that has remained unanswered after over 100 years of research on guanine: what are the crystals made of? Using solution-state and solid-state chemical techniques coupled with structural analysis by powder XRD and solid-state NMR, we compare the purine compositions and the structures of seven biogenic guanine crystals with different crystal morphologies, testing the hypothesis that intracrystalline dopants influence the crystal shape. We find that biogenic “guanine” crystals are not pure crystals but molecular alloys (aka solid solutions and mixed crystals) of guanine, hypoxanthine, and sometimes xanthine. Guanine host crystals occlude homogeneous mixtures of other purines, sometimes in remarkably large amounts (up to 20% of hypoxanthine), without significantly altering the crystal structure of the guanine host. We find no correlation between the biogenic crystal morphology and dopant content and conclude that dopants do not dictate the crystal morphology of the guanine host. The ability of guanine crystals to host other molecules enables animals to build physiologically “cheaper” crystals from mixtures of metabolically available purines, without impeding optical functionality. The exceptional levels of doping in biogenic guanine offer inspiration for the design of mixed molecular crystals that incorporate multiple functionalities in a single material

Spectroscopic Discrimination of Sorghum Silica Phytoliths

Grasses accumulate silicon in the form of silicic acid, which is precipitated as amorphous silica in microscopic particles termed phytoliths. These particles comprise a variety of morphologies according to the cell type in which the silica was deposited. Despite the evident morphological differences, phytolith chemistry has mostly been analysed in bulk samples, neglecting differences between the varied types formed in the same species. In this work, we extracted leaf phytoliths from mature plants of Sorghum bicolor (L.) Moench. Using solid state NMR and thermogravimetric analysis, we show that the extraction methods alter greatly the silica molecular structure, its condensation degree and the trapped organic matter. Measurements of individual phytoliths by Raman and synchrotron FTIR microspectroscopies in combination with multivariate analysis separated bilobate silica cells from prickles and long cells, based on the silica molecular structures and the fraction and composition of occluded organic matter. The variations in structure and composition of sorghum phytoliths suggest that the biological pathways leading to silica deposition vary between these cell types.Peer Reviewe

Minerals in the pre-settled coral Stylophora pistillata crystallize via protein and ion changes

\u3cp\u3eAragonite skeletons in corals are key contributors to the storage of atmospheric CO\u3csub\u3e2\u3c/sub\u3e worldwide. Hence, understanding coral biomineralization/calcification processes is crucial for evaluating and predicting the effect of environmental factors on this process. While coral biomineralization studies have focused on adult corals, the exact stage at which corals initiate mineralization remains enigmatic. Here, we show that minerals are first precipitated as amorphous calcium carbonate and small aragonite crystallites, in the pre-settled larva, which then evolve into the more mature aragonitic fibers characteristic of the stony coral skeleton. The process is accompanied by modulation of proteins and ions within these minerals. These findings may indicate an underlying bimodal regulation tactic adopted by the animal, with important ramification to its resilience or vulnerability toward a changing environment.\u3c/p\u3

A REDOR ssNMR Investigation of the Role of an N‑Terminus Lysine in R5 Silica Recognition

Diatoms are unicellular algae that construct cell walls called frustules by the precipitation of silica, using special proteins that order the silica into a wide variety of nanostructures. The diatom species <i>Cylindrotheca fusiformis</i> contains proteins called silaffins within its frustules, which are believed to assemble into supramolecular matrices that serve as both accelerators and templates for silica deposition. Studying the properties of these biosilicification proteins has allowed the design of new protein and peptide systems that generate customizable silica nanostructures, with potential generalization to other mineral systems. It is essential to understand the mechanisms of aggregation of the protein and its coprecipitation with silica. We continue previous investigations into the peptide R5, derived from silaffin protein sil1p, shown to independently catalyze the precipitation of silica nanospheres in vitro. We used the solid-state NMR technique ¹³C­{²⁹Si} and ¹⁵N­{²⁹Si} REDOR to investigate the structure and interactions of R5 in complex with coprecipitated silica. These experiments are sensitive to the strength of magnetic dipole–dipole interactions between the ¹³C nuclei in R5 and the ²⁹Si nuclei in the silica and thus yield distance between parts of R5 and ²⁹Si in silica. Our data show strong interactions and short internuclear distances of 3.74 ± 0.20 Å between ¹³CO Lys3 and silica. On the other hand, the C_α and C_β nuclei show little or no interaction with ²⁹Si. This selective proximity between the K3 CO and the silica supports a previously proposed mechanism of rapid silicification of the antimicrobial peptide KSL (KKVVFKVKFK) through an imidate intermediate. This study reports for the first time a direct interaction between the N-terminus of R5 and silica, leading us to believe that the N-terminus of R5 is a key component in the molecular recognition process and a major factor in silica morphogenesis

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The interplay between calcite crystal nucleation on polydiacetylene template and its amorphization by phosphoserine

Organisms use a diverse range of organic-inorganic hybrid materials for a variety of purposes, including mechanical support, navigation and protection. These materials are mostly crystalline and are characterized by unique composition, polymorph, crystallite size, shape and crystallographic orientation. The crystalline biominerals are generally formed through amorphous, hydrated transient minerals, but in some, the amorphous phases are stable and persist. Using a biomimetic approach, we address aspects of biological mineralization in vitro and gain insight into the processes and interactions that play roles in the natural systems, in-vivo. In this work, we demonstrate two essential but conflicting methods that are likely to act simultaneously in many mineralizing systems. These are directed crystal nucleation on organic templates, and on the other hand, crystal inhibition to produce the transient amorphous phase. The experimental method in this project mimics aspects of biomineralization processes of calcium carbonate (CaCO3) nucleation. Polydiacetylene (PDA) – a robust, linear conjugated polymer, made from amphiphilic long-chain diacetylene monomers, which upon surface compression, followed by UV polymerization form an ultrathin, stable monolayer structure. PDA simulates the organic template for the CaCO3 crystallization in our experimental system in that it exposed a dense array of acidic groups in well-defined orientation and being a semi-rigid template surface. On PDA templates, calcite crystals nucleate from a (01.2) face and in every single domain of the PDA film they are all coaligned with the crystals\u27 a-axes oriented parallel to the polymer backbone. Supersaturated solutions for CaCO3were prepared either by mixing CaCl2 and Na2CO3, or by bubbling CO2 into CaCO3 suspension, or by slow diffusion of ammonium carbonate into CaCl2 solution in a desiccator. Phosphoserine (P-ser) was added to CaCO3 deposition systems as a crystallization inhibitor, which results in amorphous calcium carbonate (ACC) deposition. The phosphate groups substitute a part of the carbonate groups during the deposition and this way, inhibit the crystallization process. Various concentrations of P-ser in deposition system on PDA templates result in different morphologies and degrees of crystallinity of CaCO3. In this biomimetic system, we demonstrate the conflicting, yet simultaneous influences on biological crystal formation, namely the ordered template and crystal nucleation and crystal inhibition