Elucidating the mitochondrial proteome of Toxoplasma gondii reveals the presence of a divergent cytochrome c oxidase

The mitochondrion of apicomplexan parasites is critical for parasite survival, although the full complement of proteins that localize to this organelle has not been defined. Here we undertake two independent approaches to elucidate the mitochondrial proteome of the apicomplexan Toxoplasma gondii. We identify approximately 400 mitochondrial proteins, many of which lack homologs in the animals that these parasites infect, and most of which are important for parasite growth. We demonstrate that one such protein, termed TgApiCox25, is an important component of the parasite cytochrome c oxidase (COX) complex. We identify numerous other apicomplexan-specific components of COX, and conclude that apicomplexan COX, and apicomplexan mitochondria more generally, differ substantially in their protein composition from the hosts they infect. Our study highlights the diversity that exists in mitochondrial proteomes across the eukaryotic domain of life, and provides a foundation for defining unique aspects of mitochondrial biology in an important phylum of parasites.This work was supported by a Discovery Grant and QEII fellowship from the Australian Research Council (ARC DP110103144) to GvD

Work functions, ionization potentials, and in-between: Scaling relations based on the image charge model

We revisit a model in which the ionization energy of a metal particle is associated with the work done by the image charge force in moving the electron from infinity to a small cut-off distance just outside the surface. We show that this model can be compactly, and productively, employed to study the size dependence of electron removal energies over the range encompassing bulk surfaces, finite clusters, and individual atoms. It accounts in a straightforward manner for the empirically known correlation between the atomic ionization potential (IP) and the metal work function (WF), IP/WF$\sim$2. We formulate simple expressions for the model parameters, requiring only a single property (the atomic polarizability or the nearest neighbor distance) as input. Without any additional adjustable parameters, the model yields both the IP and the WF within $\sim$10% for all metallic elements, as well as matches the size evolution of the ionization potentials of finite metal clusters for a large fraction of the experimental data. The parametrization takes advantage of a remarkably constant numerical correlation between the nearest-neighbor distance in a crystal, the cube root of the atomic polarizability, and the image force cutoff length. The paper also includes an analytical derivation of the relation of the outer radius of a cluster of close-packed spheres to its geometric structure.Comment: Original submission: 8 pages with 7 figures incorporated in the text. Revised submission (added one more paragraph about alloy work functions): 18 double spaced pages + 8 separate figures. Accepted for publication in PR

Agarose-Based biomaterials: Opportunities and challenges in cartilage tissue engineering

The lack of adequate blood/lymphatic vessels as well as low-potential articular cartilage regeneration underlines the necessity to search for alternative biomaterials. Owing to their unique features, such as reversible thermogelling behavior and tissue-like mechanical behavior, agarose-based biomaterials have played a key role in cartilage tissue repair. Accordingly, the need for fabricating novel highly efficient injectable agarose-based biomaterials as hydrogels for restoration of injured cartilage tissue has been recognized. In this review, the resources and conspicuous properties of the agarose-based biomaterials were reviewed. First, different types of signals together with their functionalities in the maintenance of cartilage homeostasis were explained. Then, various cellular signaling pathways and their significant role in cartilage tissue engineering were overviewed. Next, the molecular structure and its gelling behavior have been discussed. Eventually, the latest advancements, the lingering challenges, and future ahead of agarose derivatives from the cartilage regeneration perspective have been discussed. © 2020 by the authors

Free vibrations of non-uniform CNT/fiber/polymer nanocomposite beams

In this paper, free vibrations of non-uniform multi-scale nanocomposite beams reinforced by carbon nanotubes (CNTs) are studied. Mori-Tanaka (MT) technique is employed to estimate the effective mechanical properties of three-phase CNT/fiber/polymer composite (CNTFPC) beam. In order to obtain the natural frequencies of structure, the governing equation is solved by means of Generalized Differential Quadrature (GDQ) approach. The accuracy and efficiency of the applied methods are studied and compared with some experimental data reported in previous published works. The influences of volume fraction and agglomeration of nanotubes, volume fraction of long fibers, and different laminate lay-ups on the natural frequency response of structure are examined

ATRPases: enzymes as catalysts for atom transfer radical polymerization

Atom transfer radical polymn. (ATRP) is a powerful synthetic tool that is commonly used in polymer chem. This controlled radical polymn. leads to the synthesis of well-defined, end-functionalized polymers with complex mol. architectures. We discovered that heme proteins such as Hb (Hb) and horseradish peroxidase (HRP) catalyze the polymn. of vinyl monomers in the presence of ATRP-initiators and the reducing agent ascorbic acid under conditions typical of activators regenerated by electron transfer (ARGET) ATRP. We call this novel biocatalytic activity ATRPase activity. It yields bromine-terminated polymer chains with polydispersities as low as 1.2. The reaction kinetics were of first order, and for some monomers such as poly(ethylene glycol) Me ether acrylate (PEGA), the polymers' mol. wts. increased with conversion. These findings show that ATRPase activity is a controlled polymn. that involves reversible bromine-atom transfer between the growing polymer chain and the protein. ATRPases could become 'green' alternatives to the transition metal complexes that are currently used as catalysts for ATRP, because proteins are non-toxic, derived from renewable resources, and (e.g. in the case of Hb) cheap and abundantly available

ATRPases: enzymes as catalysts for atom transfer radical polymerization

Atom transfer radical polymn. (ATRP) is a powerful synthetic tool that is commonly used in polymer chem. This controlled radical polymn. leads to the synthesis of well-defined, end-functionalized polymers with complex mol. architectures. We discovered that heme proteins such as Hb (Hb) and horseradish peroxidase (HRP) catalyze the polymn. of vinyl monomers in the presence of ATRP-initiators and the reducing agent ascorbic acid under conditions typical of activators regenerated by electron transfer (ARGET) ATRP. We call this novel biocatalytic activity ATRPase activity. It yields bromine-terminated polymer chains with polydispersities as low as 1.2. The reaction kinetics were of first order, and for some monomers such as poly(ethylene glycol) Me ether acrylate (PEGA), the polymers' mol. wts. increased with conversion. These findings show that ATRPase activity is a controlled polymn. that involves reversible bromine-atom transfer between the growing polymer chain and the protein. ATRPases could become 'green' alternatives to the transition metal complexes that are currently used as catalysts for ATRP, because proteins are non-toxic, derived from renewable resources, and (e.g. in the case of Hb) cheap and abundantly available