A four amino acid peptide containing the β-turn template dPro-Pro in the middle and two cysteines (Cys) in the terminal positions (CdPPC) has been synthesized and its mercury(II) coordination properties studied using different spectroscopic methods. The UV-vis, CD, (199m)Hg PAC, and Raman spectroscopic studies indicate the binding of Hg(II) to the two Cys, forming the dithiolatemercury(II) complex Hg(CdPPC). Electrospray ionization mass spectrometry corroborates the 1:1 complex formation. A log K = 40.0 was determined for the formation constant of the Hg(CdPPC) complex using competition potentiometric studies. Replacement of the dPro-Pro motif by a Pro-Pro unit generated a peptide (CPPC) capable of forming a similar species [Hg(CPPC)] but showing a lower affinity for Hg(II) (at least 3-3.5 orders of magnitude lower). The introduction of the dPro-Pro motif is crucial to induce the folding of the CdPPC peptide into a β-turn, preorganizing the two Cys for mercury(II) coordination. While the simple dPro-Pro unit mimics the overall preorganization achieved by the protein scaffold in metalloproteins containing the conserved metal ion chelation unit CXXC, the high thiophilicity of this metal stabilizes the final complex in a wide pH range (1.1-10). Using computational modeling, the structures of two conformers for Hg(CdPPC) have been optimized that differ mainly in the orientation of the plane containing S-Hg-S with respect to the anchoring C atoms.

A novel heterometallic oxalate-based compound of the formula {[Co(bpy)3][Mn2(C2O4)3]·H2O}n (1; bpy = 2,2'-bipyridine) was synthesized and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction (XRD), and magnetization measurement. The molecular structure of 1 is made of a three-dimensional (3D) anionic network, [Mn2(C2O4)3]n(2n-), and tris-chelated cations [Co(bpy)3](2+) occupying the vacancies of the framework. Splitting between the zero-field-cooled (ZFC) and field-cooled (FC) branches of susceptibility below the small peak at 13 K indicates magnetic ordering. Compound 1 was used as a single-source precursor for the formation of the mixed-metal oxide CoMn2O4. This conversion via thermal decomposition was explored by thermal analysis (TGA and DTA), IR spectroscopy, powder XRD, and magnetic susceptibility measurement. From refined structural parameters, it could be seen that the spinel obtained by the thermal treatment of 1 at 800 °C is characterized by the inversion parameter δ = 21%, and therefore the structural formula at room temperature can be written as (tet)[Co(0.79)Mn(0.21)](oct)[Co(0.105)Mn(0.895)]2O4. The temperature dependence of magnetization for CoMn2O4 points to at least three magnetic phases: the ferrimagnetic state is observed below 83 K, and up to 180 K blocking of the magnetic moments of nanocrystallites of 31 nm appears, transforming to paramagnetic-like behavior above 180 K. Microstructural characterization of the CoMn2O4 sample was carried out by means of XRD line-broadening analysis.

New hepatitis B virions released from infected hepatocytes are the result of an intricate maturation process that starts with the formation of the nucleocapsid providing a confined space where the viral DNA genome is synthesized via reverse transcription. Virion assembly is finalized by the enclosure of the icosahedral nucleocapsid within a heterogeneous envelope. The latter contains integral membrane proteins of three sizes, collectively known as hepatitis B surface antigen, and adopts multiple conformations in the course of the viral life cycle. The nucleocapsid conformation depends on the reverse transcription status of the genome, which in turn controls nucleocapsid interaction with the envelope proteins for virus exit. In addition, after secretion the virions undergo a distinct maturation step during which a topological switch of the large envelope protein confers infectivity. Here we review molecular determinants for envelopment and models that postulate molecular signals encoded in the capsid scaffold conducive or adverse to the recruitment of envelope proteins. Expected final online publication date for the Annual Review of Virology, Volume 7 is September 29, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Metallothioneins (MTs) are crucial players in metal-related physiological processes. They are characterized by a high cysteine content and unique metal binding properties resulting in specific metal-thiolate clusters formation. Here we present the first NMR solution structure of a Pseudomonas MT, PflQ2 MT, using the strain P. fluorescens Q2-87. It consists of a metal binding domain and an intrinsically disordered C-terminal tail, that was not observed in other MTs so far. While not influencing the structure or function of the metal binding domain, the tail contains a potential binding motif that might be important in so far undiscovered biological interactions. Unusual is the different metal binding capacity for three ZnIIversus four CdII ions that results in two novel metal-cluster topologies. Nevertheless, the affinity for the fourth CdII ion is reduced due to transient coordination. PflQ2 MT contains an unusually large number of four histidine residues, of which only one is involved in metal ion binding. The three non-coordinating histidine residues influence neither the protein fold nor the stability in vitro. We demonstrate that reinstatement of a second coordinating histidine residue, observed for cyanobacterial MTs, in place of a non-coordinating residue in Pseudomonas MTs, decreases the kinetic lability of the cluster, while preserving the overall metal ion binding stability and the protein fold. Since high thermodynamic stability combined with high kinetic lability of metal binding are mechanistic features critical for the function of MTs, the observed replacement might be advantageous for Pseudomonas MTs with respect to metal ion handling in vivo.

The sizes of CoMnO nanoparticles can easily be tuned, from 40 to 8 nm, depending on the temperature of decomposition of the single-source molecular precursor {[Co(bpy)][Mn(CO)]·HO}. The structural features of the CoMnO spinel are also affected by the heat treatment temperature, showing a pronounced expansion of unit cell parameters as a consequence of thermally induced cation redistribution between tetrahedral and octahedral sites. Moreover, the magnetic behavior of CoMnO was successfully tailored as well; depending on the heat treatment, it is possible to switch between the superparamagnetic and ferrimagnetic ordering and to tailor the magnetic transition temperatures, i.e., the boundaries between the hard and soft magnetic behavior.

Metallothioneins (MTs) are low molecular weight, Cys-rich proteins that sequester both essential and non-essential metal ions. Despite being highly conserved in the Pseudomonas genus of Gram-negative bacteria, knowledge of their physiological function in this species is scarce. Using the strain P. fluorescens Q2-87 as a model organism, we investigated the role of a conserved MT in zinc homeostasis, cadmium detoxification as well as its implications in stress response. We show that MT expression is only induced in the stationary phase and provides a fitness benefit for long-term starvation survival, while it is not required for metal resistance and acquisition, oxidative or nitrosative stress response, biofilm formation or motility.

Naturally occurring Ser/Cys variations in Pseudomonas metallothioneinss affect intra-cluster dynamics rather than binding capacity.

In nature, thiolate-based systems are the primary targets of divalent mercury (Hg II ) toxicity. The formation of Hg (Cys) x cores in catalytic and structural protein centers mediates mercury's toxic effects and ultimately leads to cellular damage. Multiple studies have revealed distinct Hg IIthiolate coordination preferences, among which linear Hg II complexes are the most commonly observed in solution at physiological pH. Trigonal or tetrahedral geometries are formed at basic pH or in tight intraprotein Cys-rich metal sites. So far, no interprotein tetrahedral Hg II complex formed at neutral pH has been reported. Rad50 protein is a part of the multiprotein MRN complex, a major player in DNA damage-repair processes. Its central region consists of a conserved CXXC motif that enables dimerization of two Rad50 molecules by coordinating Zn II . Dimerized motifs form a unique interprotein zinc hook domain (Hk) that is critical for the biological activity of the MRN. Using a series of lengthdifferentiated peptide models of the Pyrococcus furiosus zinc hook domain, we investigated its interaction with Hg II . Using UV-Vis, CD, PAC, and 199 Hg NMR spectroscopies as well as anisotropy decay, we discovered that all Rad50 fragments preferentially form homodimeric Hg(Hk) 2 species with a distorted tetrahedral HgS 4 coordination environment at physiological pH; this is the first example of an interprotein mercury site displaying tetrahedral geometry in solution. At higher Hg II content, monomeric HgHk complexes with linear geometry are formed. The Hg(Cys) 4 core of Rad50 is extremely stable and does not compete with cyanides, NAC, or DTT. Applying ITC, we found that the stability constant of the Rad50 Hg(Hk) 2 complex is approximately three orders of magnitude higher than those of the strongest Hg II complexes known to date.