1
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Wu T, Hornsby M, Zhu L, Yu JC, Shokat KM, Gestwicki JE. Protocol for performing and optimizing differential scanning fluorimetry experiments. STAR Protoc 2023; 4:102688. [PMID: 37943662 PMCID: PMC10663957 DOI: 10.1016/j.xpro.2023.102688] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Revised: 06/21/2023] [Accepted: 10/12/2023] [Indexed: 11/12/2023] Open
Abstract
Differential scanning fluorimetry (DSF) is a widely used technique for determining the apparent melting temperature (Tma) of a purified protein. Here, we present a protocol for performing and optimizing DSF experiments. We describe steps for designing and performing the experiment, analyzing data, and optimization. We provide benchmarks for typical Tmas and ΔTmas, standard assay conditions, and upper and lower limits of commonly altered experimental variables. We also detail common pitfalls of DSF and ways to avoid, identify, and overcome them.
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Affiliation(s)
- Taiasean Wu
- Department of Pharmaceutical Chemistry and the Institute for Neurodegenerative Disease, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Michael Hornsby
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 941583, USA
| | - Lawrence Zhu
- Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Joshua C Yu
- Department of Pharmaceutical Chemistry and the Institute for Neurodegenerative Disease, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Kevan M Shokat
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 941583, USA; Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA; Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Jason E Gestwicki
- Department of Pharmaceutical Chemistry and the Institute for Neurodegenerative Disease, University of California, San Francisco, San Francisco, CA 94158, USA.
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2
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Abstract
Aggressive diagnostic testing remains an indispensable strategy for health and aged care facilities to prevent the transmission of SARS-CoV-2 in vulnerable populations. The preferred diagnostic platform has shifted towards COVID-19 rapid antigen tests (RATs) to identify the most infectious individuals. As such, RATs are being manufactured faster than at any other time in our history yet lack the relevant quantitative analytics required to inform on absolute analytical sensitivity enabling manufacturers to maintain high batch-to-batch reproducibility, and end-users to accurately compare brands for decision making. Here, we describe a novel reference standard to measure and compare the analytical sensitivity of RATs using a recombinant GFP-tagged nucleocapsid protein (NP-GFP). Importantly, we show that the GFP tag does not interfere with NP detection and provides several advantages affording streamlined protein expression and purification in high yields as well as faster, cheaper and more sensitive quality control measures for post-production assessment of protein solubility and stability. Ten commercial COVID-19 RATs were evaluated and ranked using NP-GFP as a reference standard. Analytical sensitivity data of the selected devices as determined with NP-GFP did not correlate with those reported by the manufacturers using the median tissue culture infectious dose (TCID50) assay. Of note, TCID50 discordance has been previously reported. Taken together, our results highlight an urgent need for a reliable reference standard for evaluation and benchmarking of the analytical sensitivity of RAT devices. NP-GFP is a promising candidate as a reference standard that will ensure that RAT performance is accurately communicated to healthcare providers and the public.
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3
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Radford HM, Toft CJ, Sorenson AE, Schaeffer PM. Inhibition of Replication Fork Formation and Progression: Targeting the Replication Initiation and Primosomal Proteins. Int J Mol Sci 2023; 24:ijms24108802. [PMID: 37240152 DOI: 10.3390/ijms24108802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 05/02/2023] [Accepted: 05/09/2023] [Indexed: 05/28/2023] Open
Abstract
Over 1.2 million deaths are attributed to multi-drug-resistant (MDR) bacteria each year. Persistence of MDR bacteria is primarily due to the molecular mechanisms that permit fast replication and rapid evolution. As many pathogens continue to build resistance genes, current antibiotic treatments are being rendered useless and the pool of reliable treatments for many MDR-associated diseases is thus shrinking at an alarming rate. In the development of novel antibiotics, DNA replication is still a largely underexplored target. This review summarises critical literature and synthesises our current understanding of DNA replication initiation in bacteria with a particular focus on the utility and applicability of essential initiation proteins as emerging drug targets. A critical evaluation of the specific methods available to examine and screen the most promising replication initiation proteins is provided.
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Affiliation(s)
- Holly M Radford
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
| | - Casey J Toft
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
| | - Alanna E Sorenson
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
| | - Patrick M Schaeffer
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
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4
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Sorenson AE, Schaeffer PM. Real-Time Temperature Sensing Using a Ratiometric Dual Fluorescent Protein Biosensor. BIOSENSORS 2023; 13:338. [PMID: 36979550 PMCID: PMC10046200 DOI: 10.3390/bios13030338] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Revised: 02/27/2023] [Accepted: 03/02/2023] [Indexed: 06/18/2023]
Abstract
Accurate temperature control within biological and chemical reaction samples and instrument calibration are essential to the diagnostic, pharmaceutical and chemical industries. This is particularly challenging for microlitre-scale reactions typically used in real-time PCR applications and differential scanning fluorometry. Here, we describe the development of a simple, inexpensive ratiometric dual fluorescent protein temperature biosensor (DFPTB). A combination of cycle three green fluorescent protein and a monomeric red fluorescent protein enabled the quantification of relative temperature changes and the identification of temperature discrepancies across a wide temperature range of 4-70 °C. The maximal sensitivity of 6.7% °C-1 and precision of 0.1 °C were achieved in a biologically relevant temperature range of 25-42 °C in standard phosphate-buffered saline conditions at a pH of 7.2. Good temperature sensitivity was achieved in a variety of biological buffers and pH ranging from 4.8 to 9.1. The DFPTB can be used in either purified or mixed bacteria-encapsulated formats, paving the way for in vitro and in vivo applications for topologically precise temperature measurements.
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5
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Yao H, Cai H, Li D. Fluorescence-Detection Size-Exclusion Chromatography-Based Thermostability Assay for Membrane Proteins. Methods Mol Biol 2023; 2564:299-315. [PMID: 36107350 DOI: 10.1007/978-1-0716-2667-2_16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Green fluorescent proteins (GFPs) have lightened up almost every aspect of biological research including protein sciences. In the field of membrane protein structural biology, GFPs have been used widely to monitor membrane protein localization, expression level, the purification process and yield, and the stability inside the cells and in the test tube. Of particular interest is the fluorescence-detector size-exclusion chromatography-based thermostability assay (FSEC-TS). By simple heating and FSEC, the generally applicable method allows rapid assessment of the thermostability of GFP-fused membrane proteins without purification. Here we describe the experimental details and some typical results for the FSEC-TS method.
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Affiliation(s)
| | | | - Dianfan Li
- CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, Shanghai, China.
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6
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Onufriev AV. Biologically relevant small variations of intra-cellular pH can have significant effect on stability of protein-DNA complexes, including the nucleosome. Front Mol Biosci 2023; 10:1067787. [PMID: 37143824 PMCID: PMC10151541 DOI: 10.3389/fmolb.2023.1067787] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Accepted: 01/16/2023] [Indexed: 05/06/2023] Open
Abstract
Stability of a protein-ligand complex may be sensitive to pH of its environment. Here we explore, computationally, stability of a set of protein-nucleic acid complexes using fundamental thermodynamic linkage relationship. The nucleosome, as well as an essentially random selection of 20 protein complexes with DNA or RNA, are included in the analysis. An increase in intra-cellular/intra-nuclear pH destabilizes most complexes, including the nucleosome. We propose to quantify the effect by ΔΔG0.3-the change in the binding free energy due to pH increase of 0.3 units, corresponding to doubling of the H + activity; variations of pH of this amplitude can occur in living cells, including in the course of the cell cycle, and in cancer cells relative to normal ones. We suggest, based on relevant experimental findings, a threshold of biological significance of 1 2 k B T ( ∼ 0.3 k c a l / m o l ) for changes of stability of chromatin-related protein-DNA complexes: a change in the binding affinity above the threshold may have biological consequences. We find that for 70% of the examined complexes, Δ Δ G 0.3 > 1 2 k B T (for 10%, ΔΔG0.3 is between 3 and 4 k B T). Thus, small but relevant variations of intra-nuclear pH of 0.3 may have biological consequences for many protein-nucleic acid complexes. The binding affinity between the histone octamer and its DNA, which directly affects the DNA accessibility in the nucleosome, is predicted to be highly sensitive to intra-nuclear pH. A variation of 0.3 units results in ΔΔG0.3 ∼ 10k B T ( ∼ 6 k c a l / m o l ) ; for spontaneous unwrapping of 20 bp long entry/exit fragments of the nucleosomal DNA, ΔΔG0.3 = 2.2k B T; partial disassembly of the nucleosome into the tetrasome is characterized by ΔΔG0.3 = 5.2k B T. The predicted pH -induced modulations of the nucleosome stability are significant enough to suggest that they may have consequences relevant to the biological function of the nucleosome. Accessibility of the nucleosomal DNA is predicted to positively correlate with pH variations during the cell cycle; an increase in intra-cellular pH seen in cancer cells is predicted to lead to a more accessible nucleosomal DNA; a drop in pH associated with apoptosis is predicted to make nucleosomal DNA less accessible. We speculate that processes that depend on accessibility to the DNA in the nucleosomes, such as transcription or DNA replication, might become upregulated due to relatively small, but nevertheless realistic increases of intra-nuclear pH.
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Affiliation(s)
- Alexey V. Onufriev
- Department of Physics, Virginia Tech, Blacksburg, Blacksburg, VA, United States
- Department of Computer Science, Virginia Tech, Blacksburg, Blacksburg, VA, United States
- Center from Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA, United States
- *Correspondence: Alexey V. Onufriev,
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7
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Toft CJ, Sorenson AE, Schaeffer PM. A soft Tus-Ter interaction is hiding a fail-safe lock in the replication fork trap of Dickeya paradisiaca. Microbiol Res 2022; 263:127147. [PMID: 35914414 DOI: 10.1016/j.micres.2022.127147] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 07/26/2022] [Accepted: 07/26/2022] [Indexed: 11/18/2022]
Abstract
A variety of replication fork traps have recently been characterised in Enterobacterales, unveiling two different types of architecture. Of these, the degenerate type II fork traps are commonly found in Enterobacteriaceae such as Escherichia coli. The newly characterised type I fork traps are found almost exclusively outside Enterobacteriaceae within Enterobacterales and include several archetypes of possible ancestral architectures. Dickeya paradisiaca harbours a somewhat degenerate type I fork trap with a unique Ter1 adjacent to tus gene on one side of the circular chromosome and three putative Ter2-4 sites on the other side of the fork trap. The two innermost Ter1 and Ter2 sites are only separated by 18 kb, which is the shortest distance between two innermost Ter sites of any chromosomal fork trap identified so far. Of note, the dif site is located between these two sites, coinciding with a sharp GC-skew flip. Here we examined and compared the binding modalities of E. coli and D. paradisiaca Tus proteins for these Ter sites. Surprisingly, while Ter1-3 were functional, no significant Tus binding was observed for Ter4 even in low salt conditions, which is in stark contrast with the significant non-specific protein-DNA interactions that occur with E. coli Tus. Even more surprising was the finding that D. paradisiaca Tus has a relatively moderate binding affinity to double-stranded Ter while retaining an extremely high affinity to Ter-lock sequences. Our data revealed major differences in the salt resistance and stability between the D. paradisiaca and E. coli Tus protein complexes, suggesting that while Tus protein evolution can be quite flexible regarding the initial Ter binding step, it requires a highly stringent purifying selection for its final locked complex formation.
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Affiliation(s)
- Casey J Toft
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
| | - Alanna E Sorenson
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
| | - Patrick M Schaeffer
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia.
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8
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Xu Y, Dang S. Recent Technical Advances in Sample Preparation for Single-Particle Cryo-EM. Front Mol Biosci 2022; 9:892459. [PMID: 35813814 PMCID: PMC9263182 DOI: 10.3389/fmolb.2022.892459] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Accepted: 05/12/2022] [Indexed: 11/25/2022] Open
Abstract
Cryo-sample preparation is a vital step in the process of obtaining high-resolution structures of macromolecules by using the single-particle cryo–electron microscopy (cryo-EM) method; however, cryo-sample preparation is commonly hampered by high uncertainty and low reproducibility. Specifically, the existence of air-water interfaces during the sample vitrification process could cause protein denaturation and aggregation, complex disassembly, adoption of preferred orientations, and other serious problems affecting the protein particles, thereby making it challenging to pursue high-resolution 3D reconstruction. Therefore, sample preparation has emerged as a critical research topic, and several new methods for application at various preparation stages have been proposed to overcome the aforementioned hurdles. Here, we summarize the methods developed for enhancing the quality of cryo-samples at distinct stages of sample preparation, and we offer insights for developing future strategies based on diverse viewpoints. We anticipate that cryo-sample preparation will no longer be a limiting step in the single-particle cryo-EM field as increasing numbers of methods are developed in the near future, which will ultimately benefit the entire research community.
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Affiliation(s)
- Yixin Xu
- Division of Life Science, The Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR, China
| | - Shangyu Dang
- Division of Life Science, The Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR, China
- Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China
- Center of Systems Biology and Human Health, The Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR, China
- *Correspondence: Shangyu Dang,
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9
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Toft CJ, Sorenson AE, Schaeffer PM. Rise of the terminator protein tus: A versatile tool in the biotechnologist's toolbox. Anal Chim Acta 2022; 1213:339946. [DOI: 10.1016/j.aca.2022.339946] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 05/10/2022] [Accepted: 05/12/2022] [Indexed: 02/07/2023]
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10
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Hoarau M, Suwanakitti N, Varatthan T, Thiabma R, Rattanajak R, Charoensetakul N, Redman EK, Khotavivattana T, Vilaivan T, Yuthavong Y, Kamchonwongpaisan S. Assay Development and Identification of the First Plasmodium falciparum 7,8-dihydro-6-hydroxymethylpterin-pyrophosphokinase Inhibitors. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27113515. [PMID: 35684452 PMCID: PMC9182141 DOI: 10.3390/molecules27113515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Revised: 05/23/2022] [Accepted: 05/27/2022] [Indexed: 11/24/2022]
Abstract
In the fight towards eradication of malaria, identifying compounds active against new drug targets constitutes a key approach. Plasmodium falciparum 7,8-dihydro-6-hydroxymethylpterin-pyrophosphokinase (PfHPPK) has been advanced as a promising target, as being part of the parasite essential folate biosynthesis pathway while having no orthologue in the human genome. However, no drug discovery efforts have been reported on this enzyme. In this study, we conducted a three-step screening of our in-house antifolate library against PfHPPK using a newly designed PfHPPK-GFP protein construct. Combining virtual screening, differential scanning fluorimetry and enzymatic assay, we identified 14 compounds active against PfHPPK. Compounds’ binding modes were investigated by molecular docking, suggesting competitive binding with the HMDP substrate. Cytotoxicity and in vitro ADME properties of hit compounds were also assessed, showing good metabolic stability and low toxicity. The most active compounds displayed low micromolar IC50 against drug-resistant parasites. The reported hit compounds constitute a good starting point for inhibitor development against PfHPPK, as an alternative approach to tackle the malaria parasite.
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Affiliation(s)
- Marie Hoarau
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathum Thani 12120, Thailand; (N.S.); (T.V.); (R.T.); (R.R.); (N.C.); (Y.Y.); (S.K.)
- Correspondence:
| | - Nattida Suwanakitti
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathum Thani 12120, Thailand; (N.S.); (T.V.); (R.T.); (R.R.); (N.C.); (Y.Y.); (S.K.)
| | - Thaveechai Varatthan
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathum Thani 12120, Thailand; (N.S.); (T.V.); (R.T.); (R.R.); (N.C.); (Y.Y.); (S.K.)
| | - Ratthiya Thiabma
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathum Thani 12120, Thailand; (N.S.); (T.V.); (R.T.); (R.R.); (N.C.); (Y.Y.); (S.K.)
| | - Roonglawan Rattanajak
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathum Thani 12120, Thailand; (N.S.); (T.V.); (R.T.); (R.R.); (N.C.); (Y.Y.); (S.K.)
| | - Netnapa Charoensetakul
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathum Thani 12120, Thailand; (N.S.); (T.V.); (R.T.); (R.R.); (N.C.); (Y.Y.); (S.K.)
| | - Emily K. Redman
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand; (E.K.R.); (T.V.)
| | - Tanatorn Khotavivattana
- Center of Excellence in Natural Products Chemistry, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand;
| | - Tirayut Vilaivan
- Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand; (E.K.R.); (T.V.)
| | - Yongyuth Yuthavong
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathum Thani 12120, Thailand; (N.S.); (T.V.); (R.T.); (R.R.); (N.C.); (Y.Y.); (S.K.)
| | - Sumalee Kamchonwongpaisan
- National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathum Thani 12120, Thailand; (N.S.); (T.V.); (R.T.); (R.R.); (N.C.); (Y.Y.); (S.K.)
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11
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Toft CJ, Moreau MJJ, Perutka J, Mandapati S, Enyeart P, Sorenson AE, Ellington AD, Schaeffer PM. Delineation of the Ancestral Tus-Dependent Replication Fork Trap. Int J Mol Sci 2021; 22:ijms222413533. [PMID: 34948327 PMCID: PMC8707476 DOI: 10.3390/ijms222413533] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 12/10/2021] [Accepted: 12/15/2021] [Indexed: 12/28/2022] Open
Abstract
In Escherichia coli, DNA replication termination is orchestrated by two clusters of Ter sites forming a DNA replication fork trap when bound by Tus proteins. The formation of a ‘locked’ Tus–Ter complex is essential for halting incoming DNA replication forks. However, the absence of replication fork arrest at some Ter sites raised questions about their significance. In this study, we examined the genome-wide distribution of Tus and found that only the six innermost Ter sites (TerA–E and G) were significantly bound by Tus. We also found that a single ectopic insertion of TerB in its non-permissive orientation could not be achieved, advocating against a need for ‘back-up’ Ter sites. Finally, examination of the genomes of a variety of Enterobacterales revealed a new replication fork trap architecture mostly found outside the Enterobacteriaceae family. Taken together, our data enabled the delineation of a narrow ancestral Tus-dependent DNA replication fork trap consisting of only two Ter sites.
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Affiliation(s)
- Casey J. Toft
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia; (C.J.T.); (M.J.J.M.); (A.E.S.)
- Centre of Tropical Bioinformatics and Molecular Biology, James Cook University, Douglas, QLD 4811, Australia
| | - Morgane J. J. Moreau
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia; (C.J.T.); (M.J.J.M.); (A.E.S.)
| | - Jiri Perutka
- Institute for Cell and Molecular Biology, University of Texas, Austin, TX 78712, USA; (J.P.); (S.M.); (P.E.); (A.D.E.)
| | - Savitri Mandapati
- Institute for Cell and Molecular Biology, University of Texas, Austin, TX 78712, USA; (J.P.); (S.M.); (P.E.); (A.D.E.)
| | - Peter Enyeart
- Institute for Cell and Molecular Biology, University of Texas, Austin, TX 78712, USA; (J.P.); (S.M.); (P.E.); (A.D.E.)
| | - Alanna E. Sorenson
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia; (C.J.T.); (M.J.J.M.); (A.E.S.)
| | - Andrew D. Ellington
- Institute for Cell and Molecular Biology, University of Texas, Austin, TX 78712, USA; (J.P.); (S.M.); (P.E.); (A.D.E.)
| | - Patrick M. Schaeffer
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia; (C.J.T.); (M.J.J.M.); (A.E.S.)
- Centre of Tropical Bioinformatics and Molecular Biology, James Cook University, Douglas, QLD 4811, Australia
- Correspondence: ; Tel.: +61-(0)-7-4781-4448; Fax: +61-(0)-7-4781-6078
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12
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Atsavapranee B, Stark CD, Sunden F, Thompson S, Fordyce PM. Fundamentals to function: Quantitative and scalable approaches for measuring protein stability. Cell Syst 2021; 12:547-560. [PMID: 34139165 DOI: 10.1016/j.cels.2021.05.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 04/16/2021] [Accepted: 05/07/2021] [Indexed: 12/11/2022]
Abstract
Folding a linear chain of amino acids into a three-dimensional protein is a complex physical process that ultimately confers an impressive range of diverse functions. Although recent advances have driven significant progress in predicting three-dimensional protein structures from sequence, proteins are not static molecules. Rather, they exist as complex conformational ensembles defined by energy landscapes spanning the space of sequence and conditions. Quantitatively mapping the physical parameters that dictate these landscapes and protein stability is therefore critical to develop models that are capable of predicting how mutations alter function of proteins in disease and informing the design of proteins with desired functions. Here, we review the approaches that are used to quantify protein stability at a variety of scales, from returning multiple thermodynamic and kinetic measurements for a single protein sequence to yielding indirect insights into folding across a vast sequence space. The physical parameters derived from these approaches will provide a foundation for models that extend beyond the structural prediction to capture the complexity of conformational ensembles and, ultimately, their function.
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Affiliation(s)
| | - Catherine D Stark
- Department of Biochemistry, Stanford University, Stanford, CA 94305, USA; ChEM-H, Stanford University, Stanford, CA 94305, USA
| | - Fanny Sunden
- Department of Biochemistry, Stanford University, Stanford, CA 94305, USA
| | - Samuel Thompson
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA.
| | - Polly M Fordyce
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; ChEM-H, Stanford University, Stanford, CA 94305, USA; Department of Genetics, Stanford University, Stanford, CA 94305, USA; Chan Zuckerberg Biohub, San Francisco, CA 94110, USA.
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13
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Sorenson AE, Schaeffer PM. High-Throughput Differential Scanning Fluorimetry of GFP-Tagged Proteins. Methods Mol Biol 2020; 2089:69-85. [PMID: 31773648 DOI: 10.1007/978-1-0716-0163-1_5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/03/2023]
Abstract
Differential scanning fluorimetry is useful for a wide variety of applications including characterization of protein function, structure-activity relationships, drug screening, and optimization of buffer conditions for protein purification, enzyme activity, and crystallization. A limitation of classic differential scanning fluorimetry is its reliance on highly purified protein samples. This limitation is overcome through differential scanning fluorimetry of GFP-tagged proteins (DSF-GTP). DSF-GTP specifically measures the unfolding and aggregation of a target protein fused to GFP through its proximal perturbation effects on GFP fluorescence. As a result of this unique principle, DSF-GTP can specifically measure the thermal stability of a target protein in the presence of other proteins. Additionally, the GFP provides a unique in-assay quality control measure. Here, we describe the workflow, steps, and important considerations for executing a DSF-GTP experiment in a 96-well plate format.
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Affiliation(s)
- Alanna E Sorenson
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD, Australia
| | - Patrick M Schaeffer
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD, Australia.
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14
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Cai H, Yao H, Li T, Hutter CAJ, Li Y, Tang Y, Seeger MA, Li D. An improved fluorescent tag and its nanobodies for membrane protein expression, stability assay, and purification. Commun Biol 2020; 3:753. [PMID: 33303987 PMCID: PMC7729955 DOI: 10.1038/s42003-020-01478-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Accepted: 11/12/2020] [Indexed: 01/08/2023] Open
Abstract
Green fluorescent proteins (GFPs) are widely used to monitor membrane protein expression, purification, and stability. An ideal reporter should be stable itself and provide high sensitivity and yield. Here, we demonstrate that a coral (Galaxea fascicularis) thermostable GFP (TGP) is by such reasons an improved tag compared to the conventional jellyfish GFPs. TGP faithfully reports membrane protein stability at temperatures near 90 °C (20-min heating). By contrast, the limit for the two popular GFPs is 64 °C and 74 °C. Replacing GFPs with TGP increases yield for all four test membrane proteins in four expression systems. To establish TGP as an affinity tag for membrane protein purification, several high-affinity synthetic nanobodies (sybodies), including a non-competing pair, are generated, and the crystal structure of one complex is solved. Given these advantages, we anticipate that TGP becomes a widely used tool for membrane protein structural studies.
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Affiliation(s)
- Hongmin Cai
- University of Chinese Academy of Sciences, National Center for Protein Science Shanghai, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, 200031, Shanghai, China
| | - Hebang Yao
- University of Chinese Academy of Sciences, National Center for Protein Science Shanghai, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, 200031, Shanghai, China
| | - Tingting Li
- University of Chinese Academy of Sciences, National Center for Protein Science Shanghai, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, 200031, Shanghai, China
| | - Cedric A J Hutter
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
| | - Yanfang Li
- University of Chinese Academy of Sciences, National Center for Protein Science Shanghai, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, 200031, Shanghai, China
| | - Yannan Tang
- University of Chinese Academy of Sciences, National Center for Protein Science Shanghai, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, 200031, Shanghai, China
| | - Markus A Seeger
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
| | - Dianfan Li
- University of Chinese Academy of Sciences, National Center for Protein Science Shanghai, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, 320 Yueyang Road, 200031, Shanghai, China.
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15
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Brillault L, Landsberg MJ. Preparation of Proteins and Macromolecular Assemblies for Cryo-electron Microscopy. Methods Mol Biol 2020; 2073:221-246. [PMID: 31612445 DOI: 10.1007/978-1-4939-9869-2_13] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Cryo-electron microscopy has become popular as the penultimate step on the road to structure determination for many proteins and macromolecular assemblies. The process of obtaining high-resolution images of a purified biomolecular complex in an electron microscope often follows a long, and in many cases exhaustive screening process in which many iterative rounds of protein purification are employed and the sample preparation procedure progressively re-evaluated in order to improve the distribution of particles visualized under the electron microscope, and thus maximize the opportunity for high-resolution structure determination. Typically, negative stain electron microscopy is employed to obtain a preliminary assessment of the sample quality, followed by cryo-EM which first requires the identification of optimal vitrification conditions. The original methods for frozen-hydrated specimen preparation developed over 40 years ago still enjoy widespread use today, although recent developments have set the scene for a future where more systematic and high-throughput approaches to the preparation of vitrified biomolecular complexes may be routinely employed. Here we summarize current approaches and ongoing innovations for the preparation of frozen-hydrated single particle specimens for cryo-EM, highlighting some of the commonly encountered problems and approaches that may help overcome these.
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Affiliation(s)
- Lou Brillault
- School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, QLD, Australia
| | - Michael J Landsberg
- School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, QLD, Australia.
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16
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Sorenson AE, Schaeffer PM. A new bivalent fluorescent fusion protein for differential Cu(II) and Zn(II) ion detection in aqueous solution. Anal Chim Acta 2019; 1101:120-128. [PMID: 32029102 DOI: 10.1016/j.aca.2019.12.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 12/06/2019] [Accepted: 12/08/2019] [Indexed: 12/15/2022]
Abstract
Simple and easy to engineer metal-sensing molecules that are capable of differentiating metal ions and producing metal-specific signals are highly desirable. Metal ions affect the thermal stability of proteins by increasing or decreasing their resistance to unfolding. This work illustrates a new strategy for designing bivalent fluorescent fusion proteins capable of differentiating metal ions in solution through their distinct effects on a protein's thermal stability. A new dual purpose metal sensor was developed consisting of biotin protein ligase (BirA) from B. pseudomallei (Bp) fused to green fluorescent protein (GFP). When coupled with differential scanning fluorimetry of GFP-tagged proteins (DSF-GTP) for signal-transduction detection, Bp BirA-GFP yields distinct protein unfolding signatures with Zn(II) and Cu(II) ions in aqueous solutions. The limit of detection of the system is ∼1 μM for both metal species. The system can be used in a variety of high-throughput assay formats including for the screening of metal-binding proteins and chelators. Bp BirA-GFP has also the additional benefit of being useful in Cu(II) ion field-testing applications through simple visual observation of a temperature-dependent loss of fluorescence. Bp BirA-GFP is the first example of a 2protein-based dual purpose Cu(II) and Zn(II) ion sensor compatible with two different yet complementary signal-transduction detection systems.
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Affiliation(s)
- A E Sorenson
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD, 4811, Australia
| | - P M Schaeffer
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD, 4811, Australia.
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17
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Xie S, Wong AYH, Chen S, Tang BZ. Fluorogenic Detection and Characterization of Proteins by Aggregation‐Induced Emission Methods. Chemistry 2019; 25:5824-5847. [DOI: 10.1002/chem.201805297] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Indexed: 12/18/2022]
Affiliation(s)
- Sheng Xie
- Ming Wai Lau Centre for Reparative MedicineKarolinska Institutet Hong Kong S.A.R. China
| | - Alex Y. H. Wong
- Ming Wai Lau Centre for Reparative MedicineKarolinska Institutet Hong Kong S.A.R. China
| | - Sijie Chen
- Ming Wai Lau Centre for Reparative MedicineKarolinska Institutet Hong Kong S.A.R. China
| | - Ben Zhong Tang
- Department of Chemistry, Hong Kong Branch of Chinese National, Engineering Research Center for Tissue Restoration and ReconstructionInstitute of Molecular Functional MaterialsState Key Laboratory of NeuroscienceDivision of Biomedical Engineering, and Division of Life Science, HKUST-Shenzhen Research InstituteThe Hong Kong University of Science and Technology, Kowloon Hong Kong S.A.R. China
- NSFC Center for Luminescence from Molecular AggregatesSCUT-HKUST Joint Research InstituteState Key Laboratory of Luminescent Materials and DevicesSouth China University of Technology Guangzhou 510640 P.R. China
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18
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Rana MS, Wang X, Banerjee A. An Improved Strategy for Fluorescent Tagging of Membrane Proteins for Overexpression and Purification in Mammalian Cells. Biochemistry 2018; 57:6741-6751. [PMID: 30481009 PMCID: PMC7266526 DOI: 10.1021/acs.biochem.8b01070] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
An essential prerequisite for in vitro biochemical or structural studies is a construct that is amenable to high level expression and purification and is biochemically "well-behaved". In the field of membrane protein research, the use of green fluorescent protein (GFP) to monitor and optimize the heterologous expression in different hosts has radically changed the ease of streamlining and multiplexing the testing of a large number of candidate constructs. This is achieved by genetically fusing the fluorescent proteins to the N- or C-terminus of the proteins of interest to act as reporters which can then be followed by methods such as microscopy, spectroscopy, or in-gel fluorescence. Nonetheless, a systematic study on the effect of GFP and its spectral variants on the expression and yields of recombinant membrane proteins is lacking. In this study, we genetically appended four common fluorescent protein tags, namely, mEGFP, mVenus, mCerulean, and mCherry, to the N- or C-terminus of different membrane proteins and assessed their expression in mammalian cells by fluorescence-detection size exclusion chromatography (FSEC) and protein purification. We find that, of the four fluorescent proteins, tagging with mVenus systematically results in higher expression levels that translates to higher yields in preparative purifications, thus making a case for switching to this yellow spectral variant as a better fusion tag.
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Affiliation(s)
- Mitra S. Rana
- Cell Biology and Neurobiology Branch, National Institutes of Child Health and Human Development, National Institutes of Health, Bethesda, MD-20892
| | - Xiyu Wang
- Cell Biology and Neurobiology Branch, National Institutes of Child Health and Human Development, National Institutes of Health, Bethesda, MD-20892
| | - Anirban Banerjee
- Cell Biology and Neurobiology Branch, National Institutes of Child Health and Human Development, National Institutes of Health, Bethesda, MD-20892
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19
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Askin S, Bond TEH, Sorenson AE, Moreau MJJ, Antony H, Davis RA, Schaeffer PM. Selective protein unfolding: a universal mechanism of action for the development of irreversible inhibitors. Chem Commun (Camb) 2018; 54:1738-1741. [DOI: 10.1039/c8cc00090e] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Selective protein unfolding was combined with high-throughput differential scanning fluorimetry of GFP-tagged proteins for the identification of irreversible enzyme inhibitors.
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Affiliation(s)
- Samuel Askin
- Centre for Biodiscovery & Molecular Development of Therapeutics
- James Cook University
- 142
- James Cook Drive
- Townsville
| | - Thomas E. H. Bond
- Centre for Biodiscovery & Molecular Development of Therapeutics
- James Cook University
- 142
- James Cook Drive
- Townsville
| | - Alanna E. Sorenson
- Centre for Biodiscovery & Molecular Development of Therapeutics
- James Cook University
- 142
- James Cook Drive
- Townsville
| | - Morgane J. J. Moreau
- Centre for Biodiscovery & Molecular Development of Therapeutics
- James Cook University
- 142
- James Cook Drive
- Townsville
| | - Helma Antony
- Centre for Biodiscovery & Molecular Development of Therapeutics
- James Cook University
- 142
- James Cook Drive
- Townsville
| | - Rohan A. Davis
- Griffith Institute for Drug Discovery
- Griffith University
- Brisbane
- Australia
| | - Patrick M. Schaeffer
- Centre for Biodiscovery & Molecular Development of Therapeutics
- James Cook University
- 142
- James Cook Drive
- Townsville
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20
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A green fluorescent protein-based assay for high-throughput ligand-binding studies of a mycobacterial biotin protein ligase. Microbiol Res 2017; 205:35-39. [PMID: 28942842 DOI: 10.1016/j.micres.2017.08.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Revised: 08/23/2017] [Accepted: 08/24/2017] [Indexed: 01/06/2023]
Abstract
Biotin protein ligase (BirA) has been identified as an emerging drug target in Mycobacterium tuberculosis due to its essential metabolic role. Indeed, it is the only enzyme capable of covalently attaching biotin onto the biotin carboxyl carrier protein subunit of the acetyl-CoA carboxylase. Despite recent interest in this protein, there is still a gap in cost-effective high-throughput screening assays for rapid identification of mycobacterial BirA-targeting inhibitors. We present for the first time the cloning, expression, purification of mycobacterial GFP-tagged BirA and its application for the development of a high-throughput assay building on the principle of differential scanning fluorimetry of GFP-tagged proteins. The data obtained in this study reveal how biotin and ATP significantly increase the thermal stability (ΔTm=+16.5°C) of M. tuberculosis BirA and lead to formation of a high affinity holoenzyme complex (Kobs=7.7nM). The new findings and mycobacterial BirA high-throughput assay presented in this work could provide an efficient platform for future anti-tubercular drug discovery campaigns.
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21
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Bond TEH, Sorenson AE, Schaeffer PM. Functional characterisation of Burkholderia pseudomallei biotin protein ligase: A toolkit for anti-melioidosis drug development. Microbiol Res 2017; 199:40-48. [PMID: 28454708 DOI: 10.1016/j.micres.2017.03.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Revised: 03/06/2017] [Accepted: 03/15/2017] [Indexed: 01/17/2023]
Abstract
Burkholderia pseudomallei (Bp) is the causative agent of melioidosis. The bacterium is responsible for 20% of community-acquired sepsis cases and 40% of sepsis-related mortalities in northeast Thailand, and is intrinsically resistant to aminoglycosides, macrolides, rifamycins, cephalosporins, and nonureidopenicillins. There is no vaccine and its diagnosis is problematic. Biotin protein ligase (BirA) which is essential for fatty acid synthesis has been proposed as a drug target in bacteria. Very few bacterial BirA have been characterized, and a better understanding of these enzymes is necessary to further assess their value as drug targets. BirA within the Burkholderia genus have not yet been investigated. We present for the first time the cloning, expression, purification and functional characterisation of the putative Bp BirA and orthologous B. thailandensis (Bt) biotin carboxyl carrier protein (BCCP) substrate. A GFP-tagged Bp BirA was produced and applied for the development of a high-throughput (HT) assay based on our differential scanning fluorimetry of GFP-tagged proteins (DSF-GTP) principle as well as an electrophoretic mobility shift assay. Our biochemical data in combination with the new HT DSF-GTP and biotinylation activity assay could facilitate future drug screening efforts against this drug-resistant organism.
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Affiliation(s)
- Thomas E H Bond
- Comparative Genomics Centre, James Cook University, DB21, James Cook Drive, Townsville, QLD 4811, Australia
| | - Alanna E Sorenson
- Comparative Genomics Centre, James Cook University, DB21, James Cook Drive, Townsville, QLD 4811, Australia
| | - Patrick M Schaeffer
- Comparative Genomics Centre, James Cook University, DB21, James Cook Drive, Townsville, QLD 4811, Australia.
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22
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Acyl carrier protein is a bacterial cytoplasmic target of cationic antimicrobial peptide LL-37. Biochem J 2015; 470:243-53. [PMID: 26188040 DOI: 10.1042/bj20150432] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 07/16/2015] [Indexed: 11/17/2022]
Abstract
In addition to membrane disruption, the cathelicidin antimicrobial peptide (AMP) LL-37 translocates through the bacterial inner membrane to target intracellular molecules. The present study aims to identify an alternate mechanism and a cytoplasmic target of LL-37 in Francisella. LL-37 binding proteins from Francisella novicida U112 bacterial lysates were precipitated by using biotinylated LL-37 (B-LL-37) and NeutrAvidin-agarose beads. Bound proteins were identified by LC-MS/MS, validated and characterized by bead pull-down assays and differential scanning fluorimetry (DSF). The cationic AMP (CAMP) LL-37 was able to interact with Francisella cytoplasmic acyl carrier protein (AcpP; FTN1340/FTT1376). Further study confirmed that LL-37 peptide could bind to AcpP and that the sheep cathelicidin SMAP-29 (Sheep Myeloid Antimicrobial Peptide 29) further increased LL-37 binding to AcpP, suggesting a synergistic effect of SMAP-29 on the binding. LL-37 could also bind to both AcpP of Escherichia coli and Bacillus anthracis, implying a mechanism of broad action of LL-37-AcpP binding. Overexpression of the acpP gene in F. novicida led to an increase in LL-37 susceptibility. LL-37 binding to AcpP changed the fatty acid composition profiles. Taken together, we identified a novel cytoplasmic target of LL-37 in Francisella, suggesting a mechanism of action of this peptide beyond membrane permeabilization. Our findings highlight a novel mechanism of antimicrobial activity of this peptide and document a previously unexplored target of α-helical CAMPs.
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23
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Differential Scanning Fluorimetry provides high throughput data on silk protein transitions. Sci Rep 2014; 4:5625. [PMID: 25004800 PMCID: PMC4088128 DOI: 10.1038/srep05625] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Accepted: 06/16/2014] [Indexed: 11/08/2022] Open
Abstract
Here we present a set of measurements using Differential Scanning Fluorimetry (DSF) as an inexpensive, high throughput screening method to investigate the folding of silk protein molecules as they abandon their first native melt conformation, dehydrate and denature into their final solid filament conformation. Our first data and analyses comparing silks from spiders, mulberry and wild silkworms as well as reconstituted ‘silk' fibroin show that DSF can provide valuable insights into details of silk denaturation processes that might be active during spinning. We conclude that this technique and technology offers a powerful and novel tool to analyse silk protein transitions in detail by allowing many changes to the silk solutions to be tested rapidly with microliter scale sample sizes. Such transition mechanisms will lead to important generic insights into the folding patterns not only of silks but also of other fibrous protein (bio)polymers.
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24
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Moreau MJJ, Schaeffer PM. Dissecting the salt dependence of the Tus–Ter protein–DNA complexes by high-throughput differential scanning fluorimetry of a GFP-tagged Tus. MOLECULAR BIOSYSTEMS 2013; 9:3146-54. [DOI: 10.1039/c3mb70426b] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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25
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Antony H, Schaeffer PM. A GFP-tagged nucleoprotein-based aggregation assay for anti-influenza drug discovery and antibody development. Analyst 2013; 138:6073-80. [DOI: 10.1039/c3an01041d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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