Towards Biological Supramolecular Chemistry: A Variety of Pocket-Templated, Individual Metal Oxide Cluster Nucleations in the Cavity of a Mo/W-Storage Protein

Synthesis and photo-/electro-catalytic properties of Keggin polyoxometalate inorganic–organic hybrid layers based on d10 metal and rigid benzo-diazole/-triazole ligands

Unusual hepta- and nona-nuclear copper/silver complexes were introduced into different Keggin cluster leading to 2-D hybrid layers, which exhibit merit photo- and electro-catalytic properties.

Structural Characterization of the Complex between Hen Egg-White Lysozyme and Zr(IV) -Substituted Keggin Polyoxometalate as Artificial Protease

Successful co-crystallization of a noncovalent complex between hen egg-white lysozyme (HEWL) and the monomeric Zr(IV) -substituted Keggin polyoxometalate (POM) (Zr1 K1), (Et2 NH2)3 [Zr(PW11 O39)] (1), has been achieved, and its single-crystal X-ray structure has been determined. The dimeric Zr(IV) -substituted Keggin-type polyoxometalate (Zr1 K2), (Et2 NH2)10 [Zr(PW11 O39 )2] (2), has been previously shown to exhibit remarkable selectivity towards HEWL hydrolysis. The reported X-ray structure shows that the hydrolytically active Zr(IV) -substituted Keggin POM exists as a monomeric species. Prior to hydrolysis, this monomer interacts with HEWL in the vicinity of the previously identified cleavage sites found at Trp28-Val29 and Asn44-Arg45, through water-mediated H-bonding and electrostatic interactions. Three binding sites are observed at the interface of the negatively charged Keggin POM and the positively charged regions of HEWL at: 1) Gly16, Tyr20, and Arg21; 2) Asn44, Arg45, and Asn46; and 3) Arg128.

Bioinspired nanoreactors for the biomineralisation of metallic-based nanoparticles for nanomedicine

This review explores the synthesis of inorganic metallic-based nanoparticles (MBNPs) (metals, alloys, metal oxides) using biological and biologically inspired nanoreactors for precipitation/crystallisation. Such nanoparticles exhibit a range of nanoscale properties such as surface plasmon resonance (nobel metals e.g. Au), fluorescence (semiconductor quantum dots e.g. CdSe) and nanomagnetism (magnetic alloys e.g. CoPt and iron oxides e.g. magnetite), which are currently the subject of intensive research for their applicability in diagnostic and therapeutic nanomedicine. For such applications, MBNPs are required to be biocompatible, of a precise size and shape for a consistent signal or output and be easily modified with biomolecules for applications. Ideally the MBNPs would be obtained via an environmentally-friendly synthetic route. A biological or biologically inspired nanoreactor synthesis of MBNPs is shown to address these issues. Biological nanoreactors for crystallizing MBNPs within cells (magnetosomes), protein cages (ferritin) and virus capsids (cowpea chlorotic mottle, cowpea mosaic and tobacco mosaic viruses), are discussed along with how these have been modified for applications and for the next generation of new materials. Biomimetic liposome, polymersome and even designed self-assembled proteinosome nanoreactors are also reviewed for MBNP crystallisation and further modification for applications. With the advent of synthetic biology, the research and understanding in this field is growing, with the goal of realising nanoreactor synthesis of MBNPs for biomedical applications within our grasp in the near future.

Hen egg-white lysozyme crystallisation: protein stacking and structure stability enhanced by a Tellurium(VI)-centred polyoxotungstate

As synchrotron radiation becomes more intense, detectors become faster and structure-solving software becomes more elaborate, obtaining single crystals suitable for data collection is now the bottleneck in macromolecular crystallography. Hence, there is a need for novel and advanced crystallisation agents with the ability to crystallise proteins that are otherwise challenging. Here, an Anderson-Evans-type polyoxometalate (POM), specifically Na6 [TeW6 O24 ]⋅22 H2 O (TEW), is employed as a crystallisation additive. Its effects on protein crystallisation are demonstrated with hen egg-white lysozyme (HEWL), which co-crystallises with TEW in the vicinity (or within) the liquid-liquid phase separation (LLPS) region. The X-ray structure (PDB ID: 4PHI) determination revealed that TEW molecules are part of the crystal lattice, thus demonstrating specific binding to HEWL with electrostatic interactions and hydrogen bonds. The negatively charged TEW polyoxotungstate binds to sites with a positive electrostatic potential located between two (or more) symmetry-related protein chains. Thus, TEW facilitates the formation of protein-protein interfaces of otherwise repulsive surfaces, and thereby the realisation of a stable crystal lattice. In addition to retaining the isomorphicity of the protein structure, the anomalous scattering of the POMs was used for macromolecular phasing. The results suggest that hexatungstotellurate(VI) has great potential as a crystallisation additive to promote both protein crystallisation and structure elucidation.

Azotobacter vinelandii metal storage protein: "classical" inorganic chemistry involved in Mo/W uptake and release processes

The release of Mo (as molybdate) from the Mo storage protein (MoSto), which is unique among all existing metalloproteins, is strongly influenced by temperature and pH value; other factors (incubation time, protein concentration, degree of purity) have minor, though significant effects. A detailed pH titration at 12 degrees C revealed that three different steps can be distinguished for the Mo-release process. A proportion of approximately 15% at pH 6.8-7.0, an additional 25% at pH 7.2-7.5 and ca. 50% (up to 90% in total) at pH 7.6-7.8. This triphasic process supports the assumption of the presence of different types of molybdenum-oxide-based clusters that exhibit different pH lability. The complete release of Mo was achieved by increasing the temperature to 30 degrees C and the pH value to >7.5. The Mo-release process does not require ATP; on the contrary, ATP prevents, or at least reduces the degree of metal release, depending on the concentration of the nucleotide. From this point of view, the intracellular ATP concentration is suggested to play-in addition to the pH value-an indirect but crucial role in controlling the extent of Mo release in the cell. The binding of molybdenum to the apoprotein (reconstitution process) was confirmed to be directly dependent on the presence of a nucleotide (preferably ATP) and MgCl2. Maximal reincorporation of Mo required 1 mM ATP, which could partly be replaced by GTP. When the storage protein was purified in the presence of ATP and MgCl2 (1 mM each), the final preparation contained 80 Mo atoms per protein molecule. Maximal metal loading (110-115 atoms/MoSto molecule) was only achieved, if Mo was first completely released from the native protein and subsequently (re-) bound under optimal reconstitution conditions: 1 h incubation at pH 6.5 and 12 degrees C in the presence of ATP, MgCl2 and excess molybdate. A corresponding tungsten-containing storage protein ("WSto") could not only be synthesized in vivo by growing cells, but could also be constructed in vitro by a metalate-ion exchange procedure by using the isolated MoSto protein. The high W content of the isolated cell-made WSto (approximately 110 atoms/protein molecule) and the relatively low amount of tungstate that was released from the protein under optimal "release conditions", demonstrates that the W-oxide-based clusters are more stable inside the protein cavity than the Mo-oxide analogues, as expected from the corresponding findings in polyoxometalate chemistry. The optimized isolation of the W-loaded protein form allowed us to get single crystals, and to determine the crystal X-ray structure. This proved that the protein contains remarkably different types of polyoxotungstates, the formation of which is templated in an unprecedented process by the different protein pockets. (Angew. Chem. Int. Ed. 2007, 46, 2408-2413).