Lumazine Synthase Protein Nanoparticle-Gd(III)-DOTA Conjugate as a T1 contrast agent for high-field MRI

With the applications of magnetic resonance imaging (MRI) at higher magnetic fields increasing, there is demand for MRI contrast agents with improved relaxivity at higher magnetic fields. Macromolecule-based contrast agents, such as protein-based ones, are known to yield significantly higher r(1) relaxivity at low fields, but tend to lose this merit when used as T-1 contrast agents (r(1)/r(2) = 0.5 similar to 1), with their r(1) decreasing and r(2) increasing as magnetic field strength increases. Here, we developed and characterized an in vivo applicable magnetic resonance (MR) positive contrast agent by conjugating Gd(III)-chelating agent complexes to lumazine synthase isolated from Aquifex aeolicus (AaLS). The r(1) relaxivity of Gd(III)-DOTA-AaLS-R108C was 16.49 mM(-1)s(-1) and its r(1)/r(2) ratio was 0.52 at the magnetic field strength of 7 T. The results of 3D MR angiography demonstrated the feasibility of vasculature imaging within 2 h of intravenous injection of the agent and a significant reduction in T-1 values were observed in the tumor region 7 h post-injection in the SCC-7 flank tumor model. Our findings suggest that Gd(III)-DOTA-AaLS-R108C could serve as a potential theranostic nanoplatform at high magnetic field strength.open0

Function of the Diiron Cluster of Escherichia coli Class Ia Ribonucleotide Reductase in Proton-Coupled Electron Transfer

The class Ia ribonucleotide reductase (RNR) from Escherichia coli employs a free-radical mechanism, which involves bidirectional translocation of a radical equivalent or “hole” over a distance of ~35 Å from the stable diferric/tyrosyl-radical (Y[subscript 122]•) cofactor in the β subunit to cysteine 439 (C[subscript 439]) in the active site of the α subunit. This long-range, intersubunit electron transfer occurs by a multistep “hopping” mechanism via formation of transient amino acid radicals along a specific pathway and is thought to be conformationally gated and coupled to local proton transfers. Whereas constituent amino acids of the hopping pathway have been identified, details of the proton-transfer steps and conformational gating within the β sununit have remained obscure; specific proton couples have been proposed, but no direct evidence has been provided. In the key first step, the reduction of Y[subscript 122]• by the first residue in the hopping pathway, a water ligand to Fe[subscript 1] of the diferric cluster was suggested to donate a proton to yield the neutral Y[subscript 122]. Here we show that forward radical translocation is associated with perturbation of the Mössbauer spectrum of the diferric cluster, especially the quadrupole doublet associated with Fe[subscript 1]. Density functional theory (DFT) calculations verify the consistency of the experimentally observed perturbation with that expected for deprotonation of the Fe[subscript 1]-coordinated water ligand. The results thus provide the first evidence that the diiron cluster of this prototypical class Ia RNR functions not only in its well-known role as generator of the enzyme’s essential Y[subscript 122]•, but also directly in catalysis.National Institutes of Health (U.S.) (GM-29595

LIF-Dependent Signaling: New Pieces in the Lego

LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine

Harnessing protein symmetry for enzyme design

Cyclic protein oligomers are common in Nature. Here we show that the central pore of the pentameric ring-forming protein lumazine synthase from Saccharomyces cerevisiae (ScLS) can be rationally engineered to catalyze a retro-aldol reaction. The C 5-symmetry of the complex was exploited to equip the protein tunnel with a ring of five closely spaced lysines adjacent to an apolar site for substrate binding. The resulting system utilizes amine catalysis to promote the cleavage of (±)-methodol to 6-methoxy-2- naphthaldehyde and acetone with a &gt;10 3-fold rate acceleration. The ease of organizing convergent functional groups within a protein pore may make the tunnels of many symmetric ring-shaped proteins useful starting points for creating designer enzymes.</p

Packing polymers in protein cages

The combination of addressable synthetic macromolecules with proteins of precise structure and function often leads to materials with unique properties, as is now shown by the efficient multi-site initiation of polymer growth inside the cavity of a virus capsi