scholarly journals Modular Structure of PACT: Distinct Domains for Binding and Activating PKR

2001 ◽  
Vol 21 (6) ◽  
pp. 1908-1920 ◽  
Author(s):  
Gregory A. Peters ◽  
Rune Hartmann ◽  
Jun Qin ◽  
Ganes C. Sen
Keyword(s):  
Protein Domain ◽  
Affinity Binding ◽  
Translation Inhibition ◽  
High Affinity ◽  
Cellular Apoptosis ◽  
Domain 3 ◽  
Function Relationship ◽  
Relationship Of

ABSTRACT PACT is a 35-kDa human protein that can directly bind and activate the latent protein kinase, PKR. Here we report that PKR activation by PACT causes cellular apoptosis in addition to PKR autophosphorylation and translation inhibition. We analyzed the structure-function relationship of PACT by measuring its ability to bind and activate PKR in vitro and in vivo. Our studies revealed that among three domains of PACT, the presence of either domain 1 or domain 2 was sufficient for high-affinity binding of PACT to PKR. On the other hand, domain 3, consisting of 66 residues, was absolutely required for PKR activation in vitro and in vivo. When fused to maltose-binding protein, domain 3 was also sufficient for efficiently activating PKR in vitro. However, it bound poorly to PKR at the physiological salt concentration and consequently could not activate it properly in vivo. As anticipated, activation of PKR by domain 3 in vivo could be restored by attaching it to a heterologous PKR-binding domain. These results demonstrated that the structure of PACT is modular: it is composed of a distinct PKR-activation domain and two mutually redundant PKR-interacting domains.

scholarly journals The Arg-Gly-Asp–Containing, Solvent-Exposed Loop of Ptr ToxA Is Required for Internalization

2008 ◽  
Vol 21 (3) ◽  
pp. 315-325 ◽  
Author(s):  
Viola A. Manning ◽  
Sara M. Hamilton ◽  
P. Andrew Karplus ◽  
Lynda M. Ciuffetti
Keyword(s):  
Phosphorylation Site ◽  
Affinity Binding ◽  
Mesophyll Cells ◽  
High Affinity ◽  
Treatment Zone ◽  
Ptr Toxa ◽  
High Affinity Binding Site ◽  
Toxin Uptake

Internalization of the proteinaceous host-selective toxin, Ptr ToxA (ToxA), into sensitive wheat mesophyll cells is correlated with toxin activity. The solvent-exposed, Arg-Gly-Asp (RGD)-containing loop of ToxA is a candidate for interaction with the plasma membrane, which is a likely prerequisite to toxin internalization. Based on the percentage of cells affected by a given number of ToxA molecules in a treatment zone, the number of ToxA molecules bound to high-affinity sites was estimated at 3 × 106 per cell and the Kd for binding was estimated to be near 1 nM. An improved heterologous expression method of proteins that contain mutations in ToxA, coupled with a newly developed semiquantitative bioassay, revealed that some amino acids in the RGD-containing loop contribute more to toxin activity than others. Protease protection assays that detect internalized protein and inhibition of toxin uptake indicated that, for each ToxA variant tested, the extent of toxin activity correlates with the amount of internalized protein. RGD-containing peptide inhibition of both activity and internalization supported these findings. These data support the hypothesis that ToxA interacts with a high-affinity binding site on wheat mesophyll cells through the RGD-containing, solvent-exposed loop, resulting in toxin internalization and eventual cell death. The inability to detect phosphorylation of ToxA in vitro and in vivo suggests that a putative CKII phosphorylation site in the RGD-containing loop is required for internalization, not phosphorylation.

scholarly journals New multiscale characterisation methodology for effective determination of isolation-structure-function relationship of extracellular vesicles

2021 ◽  
Author(s):  
Thanh Huyen Phan ◽  
Shiva Kamini Divakarla ◽  
Jia Hao Yeo ◽  
Qingyu Lei ◽  
Priyanka Tharkar ◽  
...  
Keyword(s):  
Extracellular Vesicles ◽  
Biological Effects ◽  
Dry Mass ◽  
Experimental Methodology ◽  
Wide Range ◽  
Isolation Methods ◽  
Function Relationship ◽  
Relationship Of

AbstractExtracellular vesicles (EVs) have been lauded as next generation medicines, but very few EV-based therapeutics have progressed to clinical use. Limited clinical translation is largely due to technical barriers that hamper our ability to mass-produce EVs, i.e. to isolate, purify and characterise them effectively. Technical limitations in comprehensive characterisation of EVs leads to unpredicted biological effects of EVs. Here, using a range of optical and non-optical techniques, we showed that the differences in molecular composition of EVs isolated using two isolation methods correlated with the differences in their biological function. Our results demonstrated that the isolation method determines the composition of isolated EVs at single and sub-population levels. Besides the composition, we measured for the first time the dry mass and predicted sedimentation of EVs. These parameters were shown to correlate well with the biological and functional effects of EVs on single cell and cell cultures. We anticipate that our new multiscale characterisation approach, which goes beyond traditional experimental methodology, will support fundamental understanding of EVs as well as elucidate the functional effects of EVs in in vitro and in vivo studies. Our findings and methodology will be pivotal for developing optimal isolation methods and establishing EVs as mainstream therapeutics and diagnostics. This innovative approach is applicable to a wide range of sectors including biopharma and biotechnology as well as to regulatory agencies.

scholarly journals Insights on the Quest for the Structure–Function Relationship of the Mitochondrial Pyruvate Carrier

Biology ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. 407
Author(s):  
José Edwin Neciosup Quesñay ◽  
Naomi L. Pollock ◽  
Raghavendra Sashi Krishna Nagampalli ◽  
Sarah C. Lee ◽  
Vijayakumar Balakrishnan ◽  
...  
Keyword(s):  
Molecular Structures ◽  
Computational Tools ◽  
Protein Subunits ◽  
Molecular Identity ◽  
Current State ◽  
Mitochondrial Pyruvate Carrier ◽  
Function Relationship ◽  
Relationship Of

The molecular identity of the mitochondrial pyruvate carrier (MPC) was presented in 2012, forty years after the active transport of cytosolic pyruvate into the mitochondrial matrix was first demonstrated. An impressive amount of in vivo and in vitro studies has since revealed an unexpected interplay between one, two, or even three protein subunits defining different functional MPC assemblies in a metabolic-specific context. These have clear implications in cell homeostasis and disease, and on the development of future therapies. Despite intensive efforts by different research groups using state-of-the-art computational tools and experimental techniques, MPCs’ structure-based mechanism remains elusive. Here, we review the current state of knowledge concerning MPCs’ molecular structures by examining both earlier and recent studies and presenting novel data to identify the regulatory, structural, and core transport activities to each of the known MPC subunits. We also discuss the potential application of cryogenic electron microscopy (cryo-EM) studies of MPC reconstituted into nanodiscs of synthetic copolymers for solving human MPC2.

scholarly journals Characterizing the structure-function relationship of a naturally-occurring RNA thermometer

2017 ◽  
Author(s):  
Sarai Meyer ◽  
Julius B. Lucks
Keyword(s):  
Heat Shock ◽  
Rna Structure ◽  
Structural Changes ◽  
Structural Motif ◽  
Ribosome Binding ◽  
Heat Shock Responses ◽  
Function Relationship ◽  
Relationship Of

AbstractA wide number of bacteria have been found to govern virulence and heat shock responses using temperature-sensing RNAs known as RNA thermometers. A prime example is theagsAthermometer known to regulate the production of the AgsA heat shock protein inSalmonella entericausing a “fourU” structural motif. Using the SHAPE-Seq RNA structure-probing methodin vivoandin vitro, we found that the regulator functions by a subtle shift in equilibrium RNA structure populations that lead to a partial melting of the helix containing the ribosome binding site. We also demonstrate that ribosome binding to theagsAmRNA causes changes to the thermometer structure that appear to facilitate thermometer helix unwinding. These results demonstrate how subtle RNA structural changes can govern gene expression and illuminate the function of an important bacterial regulatory motif.

scholarly journals Common and Variable Contributions of Fis Residues to High-Affinity Binding at Different DNA Sequences

2006 ◽  
Vol 188 (6) ◽  
pp. 2081-2095 ◽  
Author(s):  
Leah S. Feldman-Cohen ◽  
Yongping Shao ◽  
Derrick Meinhold ◽  
Charmi Miller ◽  
Wilfredo Colón ◽  
...  
Keyword(s):  
Dna Binding ◽  
Dna Sequences ◽  
Binding Motif ◽  
Affinity Binding ◽  
Flanking Sequence ◽  
Binding Assays ◽  
High Affinity Binding ◽  
High Affinity

ABSTRACT Fis is a nucleoid-associated protein that interacts with poorly related DNA sequences with a high degree of specificity. A difference of more than 3 orders of magnitude in apparent Kd values was observed between specific (Kd , ∼1 to 4 nM) and nonspecific (Kd , ∼4 μM) DNA binding. To examine the contributions of Fis residues to the high-affinity binding at different DNA sequences, 13 alanine substitutions were generated in or near the Fis helix-turn-helix DNA binding motif, and the resulting proteins were purified. In vitro binding assays at three different Fis sites (fis P II, hin distal, and λ attR) revealed that R85, T87, R89, K90, and K91 played major roles in high-affinity DNA binding and that R85, T87, and K90 were consistently vital for binding to all three sites. Other residues made variable contributions to binding, depending on the binding site. N84 was required only for binding to the λ attR Fis site, and the role of R89 was dramatically altered by the λ attR DNA flanking sequence. The effects of Fis mutations on fis P II or hin distal site binding in vitro generally correlated with their abilities to mediate fis P repression or DNA inversion in vivo, demonstrating that the in vitro DNA-binding effects are relevant in vivo. The results suggest that while Fis is able to recognize a minimal common set of DNA sequence determinants at different binding sites, it is also equipped with a number of residues that contribute to the binding strength, some of which play variable roles.

scholarly journals Mobilization of Chimeric oriT Plasmids by F and R100-1: Role of Relaxosome Formation in Defining Plasmid Specificity

2000 ◽  
Vol 182 (14) ◽  
pp. 4022-4027 ◽  
Author(s):  
Richard A. Fekete ◽  
Laura S. Frost
Keyword(s):  
Binding Sites ◽  
Integration Host Factor ◽  
Affinity Binding ◽  
High Affinity Binding ◽  
High Affinity ◽  
Negative Dominance ◽  
Transfer Apparatus

ABSTRACT Cleavage at the F plasmid nic site within the origin of transfer (oriT) requires the F-encoded proteins TraY and TraI and the host-encoded protein integration host factor in vitro. We confirm that F TraY, but not F TraM, is required for cleavage atnic in vivo. Chimeric plasmids were constructed which contained either the entire F or R100-1 oriT regions or various combinations of nic, TraY, and TraM binding sites, in addition to the traM gene. The efficiency of cleavage atnic and the frequency of mobilization were assayed in the presence of F or R100-1 plasmids. The ability of these chimeric plasmids to complement an F traM mutant or affect F transfer via negative dominance was also measured using transfer efficiency assays. In cases where cleavage at nic was detected, R100-1 TraI was not sensitive to the two-base difference in sequence immediately downstream of nic, while F TraI was specific for the F sequence. Plasmid transfer was detected only when TraM was able to bind to its cognate sites within oriT. High-affinity binding of TraY in cis to oriTallowed detection of cleavage at nic but was not required for efficient mobilization. Taken together, our results suggest that stable relaxosomes, consisting of TraI, -M, and -Y bound to oriT are preferentially targeted to the transfer apparatus (transferosome).

scholarly journals New Multiscale Characterization Methodology for Effective Determination of Isolation–Structure–Function Relationship of Extracellular Vesicles

2021 ◽  
Vol 9 ◽  
Author(s):  
Thanh Huyen Phan ◽  
Shiva Kamini Divakarla ◽  
Jia Hao Yeo ◽  
Qingyu Lei ◽  
Priyanka Tharkar ◽  
...  
Keyword(s):  
Extracellular Vesicles ◽  
Biological Effects ◽  
Dry Mass ◽  
Experimental Methodology ◽  
Wide Range ◽  
Isolation Methods ◽  
Function Relationship ◽  
Relationship Of

Extracellular vesicles (EVs) have been lauded as next-generation medicines, but very few EV-based therapeutics have progressed to clinical use. Limited clinical translation is largely due to technical barriers that hamper our ability to mass produce EVs, i.e., to isolate, purify, and characterize them effectively. Technical limitations in comprehensive characterization of EVs lead to unpredicted biological effects of EVs. Here, using a range of optical and non-optical techniques, we showed that the differences in molecular composition of EVs isolated using two isolation methods correlated with the differences in their biological function. Our results demonstrated that the isolation method determines the composition of isolated EVs at single and sub-population levels. Besides the composition, we measured for the first time the dry mass and predicted sedimentation of EVs. These parameters were likely to contribute to the biological and functional effects of EVs on single cell and cell cultures. We anticipate that our new multiscale characterization approach, which goes beyond traditional experimental methodology, will support fundamental understanding of EVs as well as elucidate the functional effects of EVs in in vitro and in vivo studies. Our findings and methodology will be pivotal for developing optimal isolation methods and establishing EVs as mainstream therapeutics and diagnostics. This innovative approach is applicable to a wide range of sectors including biopharma and biotechnology as well as to regulatory agencies.

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