Crystallization of a trimeric human T cell leukemia virus type 1 gp21 ectodomain fragment as a chimera with maltose-binding protein

We present a novel protein crystallization strategy, applied to the crystallization of human T cell leukemia virus type 1 (HTLV-1) transmembrane protein gp21 lacking the fusion peptide and the transmembrane domain, as a chimera with the Escherichia coli maltose binding protein (MBP). Crystals could not be obtained with a MBP/gp21 fusion protein in which fusion partners were separated by a flexible linker, but were obtained after connecting the MBP C-terminal alpha-helix to the predicted N-terminal alpha-helical sequence of gp21 via three alanine residues. The gp21 sequences conferred a trimeric structure to the soluble fusion proteins as assessed by sedimentation equilibrium and X-ray diffraction, consistent with the trimeric structures of other retroviral transmembrane proteins. The envelope protein precursor, gp62, is likewise trimeric when expressed in mammalian cells. Our results suggest that MBP may have a general application for the crystallization of proteins containing N-terminal alpha-helical sequences.

Crystal structure of human T cell leukemia virus type 1 gp21 ectodomain crystallized as a maltose-binding protein chimera reveals structural evolution of retroviral transmembrane proteins

Retroviral entry into cells depends on envelope glycoproteins, whereby receptor binding to the surface-exposed subunit triggers membrane fusion by the transmembrane protein (TM) subunit. We determined the crystal structure at 2.5-Angstrom resolution of the ectodomain of gp21, the TM from human T cell leukemia virus type 1. The gp21 fragment was crystallized as a maltose-binding protein chimera, and the maltose-binding protein domain was used to solve the initial phases by the method of molecular replacement. The structure of gp21 comprises an N-terminal trimeric coiled coil, an adjacent disulfide-bonded loop that stabilizes a chain reversal, and a C-terminal sequence structurally distinct from HIV type 1/simian immunodeficiency virus gp41 that packs against the coil in an extended antiparallel fashion. Comparison of the gp21 structure with the structures of other retroviral TMs contrasts the conserved nature of the coiled coil-forming region and adjacent disulfide-bonded loop with the variable nature of the C-terminal ectodomain segment. The structure points to these features having evolved to enable the dual roles of retroviral TMs: conserved fusion function and an ability to anchor diverse surface-exposed subunit structures to the virion envelope and infected cell surface. The structure of gp21 implies that the N-terminal fusion peptide is in close proximity to the C-terminal transmembrane domain and likely represents a postfusion conformation.

Questioning the utility of RNA-DNA chimera in gene repair.

In principle, we should be glad that Eric Kmiec and his colleagues published in Science's STKE (1) a detailed experimental protocol of their gene repair method (2, 3). However, a careful reading of their contribution raises more doubts about the method. The research published in Science five years ago by Kmiec and his colleagues was said to demonstrate that chimeric RNA-DNA oligonucleotides could correct the mutation responsible for sickle cell anemia with 50% efficiency (4). Such a remarkable result prompted many laboratories to attempt to replicate the research or utilize the method on their own systems. However, if the method worked at all, which it rarely did, the achieved efficiency was usually lower by several orders of magnitude. Now, in the Science's STKE protocol, we are given crucial information about the method and why it is so important to utilize these expensive chimeric RNA-DNA constructs. In the introduction we are told that the RNA-DNA duplex is more stable than a DNA-DNA duplex and so extends the half-life of the complexes formed between the targeted DNA and the chimeric RNA-DNA oligonucleotides. This logical explanation, however, conflicts with the statement in the section entitled "Transfection with Oligonucleotides and Plasmid DNA" that Kmiec and colleagues have recently demonstrated that classical single-stranded DNA oligonucleotides with a few protective phosphothioate linkages have a "gene repair conversion frequency rivaling that of the RNA/DNA chimera". Indeed, the research cited for that result actually states that single-stranded DNA oligonucleotides are in fact several-fold more efficient (3.7-fold) than the RNA-DNA chimeric constructs (5). If that is the case, it raises the question of why Kmiec and colleagues emphasize the importance of the RNA in their original chimeric constructs. Their own new results show that modified single-stranded DNA oligonucleotides are more effective than the expensive RNA-DNA hybrids. Moreover, the current efficiency of the gene repair by RNA-DNA hybrids, according to Kmiec and colleagues in their recent paper is only 4×10-4 even after several hours of pre-selection permitting multiplification of bacterial cells with the corrected plasmid (5). This efficiency is much lower than the 50% value reported five years ago, but is assuredly much closer to the reality.

Design of potent inhibitors of human RAD51 recombinase based on BRC motifs of BRCA2 protein: modeling and experimental validation of a chimera peptide.

We have previously shown that a 28-amino acid peptide derived from the BRC4 motif of BRCA2 tumor suppressor inhibits selectively human RAD51 recombinase (HsRad51). With the aim of designing better inhibitors for cancer treatment, we combined an in silico docking approach with in vitro biochemical testing to construct a highly efficient chimera peptide from eight existing human BRC motifs. We built a molecular model of all BRC motifs complexed with HsRad51 based on the crystal structure of the BRC4 motif-HsRad51 complex, computed the interaction energy of each residue in each BRC motif, and selected the best amino acid residue at each binding position. This analysis enabled us to propose four amino acid substitutions in the BRC4 motif. Three of these increased the inhibitory effect in vitro, and this effect was found to be additive. We thus obtained a peptide that is about 10 times more efficient in inhibiting HsRad51-ssDNA complex formation than the original peptide.

Artificial muscle: the human chimera is the future.

Severe heart failure and cerebral stroke are broadly associated with the impairment of muscular function that conventional treatments struggle to restore. New technologies enable the construction of "smart" materials that could be of great help in treating diseases where the main problem is muscle weakness. These materials "behave" similarly to biological systems, because the material directly converts energy, for example electrical energy into movement. The extension and contraction occur silently like in natural muscles. The real challenge is to transfer this amazing technology into devices that restore or replace the mechanical function of failing muscle. Cardiac assist devices based on artificial muscle technology could envelope a weak heart and temporarily improve its systolic function, or, if placed on top of the atrium, restore the atrial kick in chronic atrial fibrillation. Artificial sphincters could be used to treat urinary incontinence after prostatectomy or faecal incontinence associated with stomas. Artificial muscles can restore the ability of patients with facial paralysis due to stroke or nerve injury to blink. Smart materials could be used to construct an artificial oesophagus including peristaltic movement and lower oesophageal sphincter function to replace the diseased oesophagus thereby avoiding the need for laparotomy to mobilise stomach or intestine. In conclusion, in the near future, smart devices will integrate with the human body to fill functional gaps due to organ failure, and so create a human chimera.

Assembling a xylanase-lichenase chimera through all-atom molecular dynamics simulations

Multifunctional enzyme engineering can improve enzyme cocktails for emerging biofuel technology. Molecular dynamics through structure-based models (SB) is an effective tool for assessing the tridimensional arrangement of chimeric enzymes as well as for inferring the functional practicability before experimental validation. This study describes the computational design of a bifunctional xylanase-lichenase chimera (XylLich) using the xynA and bglS genes from Bacillus subtilis. In silico analysis of the average solvent accessible surface area (SAS) and the root mean square fluctuation (RMSF) predicted a fully functional chimera, with minor fluctuations and variations along the polypeptide chains. Afterwards, the chimeric enzyme was built by fusing the xynA and bglS genes. XylLich was evaluated through small-angle X-ray scattering (SAXS) experiments, resulting in scattering curves with a very accurate fit to the theoretical protein model. The chimera preserved the biochemical characteristics of the parental enzymes, with the exception of a slight variation in the temperature of operation and the catalytic efficiency (k cat/Km). The absence of substantial shifts in the catalytic mode of operation was also verified. Furthermore, the production of chimeric enzymes could be more profitable than producing a single enzyme separately, based on comparing the recombinant protein production yield and the hydrolytic activity achieved for XylLich with that of the parental enzymes. © 2013 Elsevier B.V. All rights reserved.

A synthetic histone pre-mRNA-U7 small nuclear RNA chimera undergoing cis cleavage in the cytoplasm of Xenopus oocytes.

The 3' processing of histone pre-mRNAs is a nuclear event in which the U7 small nuclear ribonucleoprotein (snRNP) participates as an essential trans-acting factor. We have constructed a chimeric histone-U7 RNA that when injected into the cytoplasm of Xenopus laevis oocytes assembles into a snRNP-like particle and becomes cleaved at the correct site(s). RNP assembly is a prerequisite for cleavage, but, since neither the RNA nor the RNP appreciably enter the nucleus, cleavage occurs mostly, if not exclusively, in the cytoplasm. Consistent with this, cleavage also occurs in enucleated oocytes or in oocytes which have been depleted of U7 snRNPs. Thus all necessary components for cleavage must be present in the oocyte cytoplasm. The novel cleavage occurs in cis, involving only a single molecule of chimeric RNA with its associated proteins. This reaction is equally dependent upon base pairing interactions between histone spacer sequences and the 5'-end of the U7 moiety as the natural in trans reaction. These results imply that U7 is the only snRNP required for histone RNA processing. Moreover, the chimeric RNA is expected to be useful for further studies of the cleavage and assembly mechanisms of U7 snRNP.

Activation of a Frizzled-2/β-adrenergic receptor chimera promotes Wnt signaling and differentiation of mouse F9 teratocarcinoma cells via Gαo and Gαt

The frizzled gene family of putative Wnt receptors encodes proteins that have a seven-transmembrane-spanning motif characteristic of G protein-linked receptors, though no loss-of-function studies have demonstrated a requirement for G proteins for Frizzled signaling. We engineered a Frizzled-2 chimera responsive to β-adrenergic agonist by using the ligand-binding domains of the β2-adrenergic receptor. The expectation was that the chimera would be sensitive both to drug-mediated activation and blockade, thereby circumventing the problem of purifying soluble and active Wnt ligand to activate Frizzled. Expression of the chimera in zebrafish embryos demonstrated isoproterenol (ISO)-stimulated, propranolol-sensitive calcium transients, thereby confirming the β-adrenergic nature of Wnt signaling by the chimeric receptor. Because F9 embryonic teratocarcinoma cells form primitive endoderm after stable transfection of Frizzled-2 chimera and stimulation with ISO, they were subject to depletion of G protein subunits. ISO stimulation of endoderm formation of F9 stem cells expressing the chimeric receptor was blocked by pertussis toxin and by oligodeoxynucleotide antisense to Gαo, Gαt2, and Gβ2. Our results demonstrate the requirement of two pertussis toxin-sensitive G proteins, Gαo and Gαt, for signaling by the Frizzled-2 receptor.

Hormone-regulatable neoplastic transformation induced by a Jun-estrogen receptor chimera

The v-jun oncogene encodes a nuclear DNA binding protein that functions as a transcription factor and is part of the activator protein 1 complex. Oncogenic transformation by v-jun is thought to be mediated by the aberrant expression of specific target genes. To identify such Jun-regulated genes and to explore the mechanisms by which Jun affects their expression, we have fused the full-length v-Jun and an amino-terminally truncated form of v-Jun to the hormone-binding domain of the human estrogen receptor. The two chimeric proteins function as ligand-inducible transactivators. Expression of the fusion proteins in chicken embryo fibroblasts causes estrogen-dependent transformation.

Genetic Dissection of Endocytic Trafficking in Drosophila Using a Horseradish Peroxidase-Bride of Sevenless Chimera: hook Is Required for Normal Maturation of Multivesicular Endosomes

Mutations in the hook gene alter intracellular trafficking of internalized ligands in Drosophila. To dissect this defect in more detail, we developed a new approach to visualize the pathway taken by the Bride of Sevenless (Boss) ligand after its internalization into R7 cells. A chimeric protein consisting of HRP fused to Boss (HRP-Boss) was expressed in R8 cells. This chimera was fully functional: it rescued the boss mutant phenotype, and its trafficking was indistinguishable from that of the wild-type Boss protein. The HRP activity of the chimera was used to follow HRP-Boss trafficking on the ultrastructural level through early and late endosomes in R7 cells. In both wild-type and hook mutant eye disks, HRP-Boss was internalized into R7 cells. In wild-type tissue, Boss accumulated in mature multivesicular bodies (MVBs) within R7 cells; such accumulation was not observed in hook eye disks, however. Quantitative electron microscopy revealed a loss of mature MVBs in hook mutant tissue compared with wild type, whereas more than twice as many multilammelar late endosomes were detected. Our genetic analysis indicates that Hook is required late in endocytic trafficking to negatively regulate delivery from mature MVBs to multilammelar late endosomes and lysosomes.

Trafficking, Assembly, and Function of a Connexin43-Green Fluorescent Protein Chimera in Live Mammalian CellsV⃞

To examine the trafficking, assembly, and turnover of connexin43 (Cx43) in living cells, we used an enhanced red-shifted mutant of green fluorescent protein (GFP) to construct a Cx43-GFP chimera. When cDNA encoding Cx43-GFP was transfected into communication-competent normal rat kidney cells, Cx43-negative Madin–Darby canine kidney (MDCK) cells, or communication-deficient Neuro2A or HeLa cells, the fusion protein of predicted length was expressed, transported, and assembled into gap junctions that exhibited the classical pentalaminar profile. Dye transfer studies showed that Cx43-GFP formed functional gap junction channels when transfected into otherwise communication-deficient HeLa or Neuro2A cells. Live imaging of Cx43-GFP in MDCK cells revealed that many gap junction plaques remained relatively immobile, whereas others coalesced laterally within the plasma membrane. Time-lapse imaging of live MDCK cells also revealed that Cx43-GFP was transported via highly mobile transport intermediates that could be divided into two size classes of <0.5 μm and 0.5–1.5 μm. In some cases, the larger intracellular Cx43-GFP transport intermediates were observed to form from the internalization of gap junctions, whereas the smaller transport intermediates may represent other routes of trafficking to or from the plasma membrane. The localization of Cx43-GFP in two transport compartments suggests that the dynamic formation and turnover of connexins may involve at least two distinct pathways.