Stephen J. Hagen

article

Carbohydrate and PepO control bimodality in competence development by Streptococcus mutans

Simon A. M. Underhill, Robert C. Shields, Robert A. Burne, Stephen J. Hagen

Molecular Microbiology > 112 > 5 > 1388 - 1402

In Streptococcus mutans, the alternative sigma factor ComX controls entry into genetic competence. Competence stimulating peptide (CSP) induces bimodal expression of comX, with only a fraction of the population becoming transformable. Curiously, the bimodality of comX is affected by peptides in the growth medium and by carbohydrate source. CSP elicits bimodal expression of comX in media rich in small...

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Characterization of LrgAB as a stationary phase-specific pyruvate uptake system in Streptococcus mutans

Sang-Joon Ahn, Kamal Deep, Matthew E. Turner, Ivan Ishkov, more

BMC Microbiology > 2019 > 19 > 1 > 1-15

Background Our recent ‘-omics’ comparisons of Streptococcus mutans wild-type and lrgAB-mutant revealed that this organism undergoes dynamic cellular changes in the face of multiple exogenous stresses, consequently affecting its comprehensive virulence traits. In this current study, we further demonstrate that LrgAB functions as a S. mutans pyruvate uptake system. Results S. mutans excretes pyruvate...

article

Co-Assembly Tags Based on Charge Complementarity (CATCH) for Installing Functional Protein Ligands into Supramolecular Biomaterials

Dillon T. Seroski, Antonietta Restuccia, Anthony D. Sorrentino, Kevin R. Knox, more

Cellular and Molecular Bioengineering > 2016 > 9 > 3 > 335-350

Installing folded proteins into biomaterials is gaining interest for imparting functional properties that often cannot be provided by unfolded peptides or small molecules, such as catalysis, antigen conformation, or molecular recognition. Although covalent grafting provides a simple means to immobilize proteins onto pre-formed biomaterials, amenable chemistries can alter protein bioactivity, are relatively...

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Traveling waves in response to a diffusing quorum sensing signal in spatially-extended bacterial colonies

Jessica B. Langebrake, Gabriel E. Dilanji, Stephen J. Hagen, Patrick De Leenheer

Journal of Theoretical Biology > 2014 > 363 > Complete > 53-61

In the behavior known as quorum sensing (QS), bacteria release diffusible signal molecules known as autoinducers, which by accumulating in the environment induce population-wide changes in gene expression. Although QS has been extensively studied in well-mixed systems, the ability of diffusing QS signals to synchronize gene expression in spatially extended colonies is not well understood. Here we...

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Microfluidic study of competence regulation in Streptococcus mutans: environmental inputs modulate bimodal and unimodal expression of comX

Minjun Son, Sang‐Joon Ahn, Qiang Guo, Robert A. Burne, more

Molecular Microbiology > 86 > 2 > 258 - 272

Streptococcus mutans regulates genetic competence through a complex network that receives inputs from a number of environmental stimuli, including two signalling peptides designated as CSP and XIP. The response of the downstream competence genes to these inputs shows evidence of stochasticity and bistability and has been difficult to interpret. We have used microfluidic, single‐cell methods to study...

article

Analysis of gene expression levels in individual bacterial cells without image segmentation

In Hae Kwak, Minjun Son, Stephen J. Hagen

Biochemical and Biophysical Research Communications > 2012 > 421 > 3 > 425-430

Studies of stochasticity in gene expression typically make use of fluorescent protein reporters, which permit the measurement of expression levels within individual cells by fluorescence microscopy. Analysis of such microscopy images is almost invariably based on a segmentation algorithm, where the image of a cell or cluster is analyzed mathematically to delineate individual cell boundaries. However...

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Noise and Crosstalk in the Two Quorum Sensing Channels of Vibrio Fischeri

Stephen J. Hagen, Pablo Delfino Pérez, Joel T. Weiss

Biophysical Journal > 2011 > 100 > 3 Supplement 1 > 165a

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Noise and crosstalk in two quorum-sensing inputs of Vibrio fischeri

Pablo D Pérez, Joel T Weiss, Stephen J Hagen

BMC Systems Biology > 2011 > 5 > 1 > 1-14

Background One of the puzzles in bacterial quorum sensing is understanding how an organism integrates the information gained from multiple input signals. The marine bacterium Vibrio fischeri regulates its bioluminescence through a quorum sensing mechanism that receives input from three pheromone signals, including two acyl homoserine lactone (HSL) signals. While the role of the 3-oxo-C6 homoserine...

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Bacterium in a box: sensing of quorum and environment by the LuxI/LuxR gene regulatory circuit

Stephen J. Hagen, Minjun Son, Joel T. Weiss, Jonathan H. Young

Journal of Biological Physics > 2010 > 36 > 3 > 317-327

The chemical signaling mechanism known as “bacterial quorum sensing” (QS) is normally interpreted as allowing bacteria to detect their own population density, in order to coordinate gene expression across a colony. However, the release of the chemical signal can also be interpreted as a means for one or a few cells to probe the local physical properties of their microenvironment. We have studied the...

article

Solvent Friction Changes the Folding Pathway of the Tryptophan Zipper TZ2

Ranjani Narayanan, Leslie Pelakh, Stephen J. Hagen

Journal of Molecular Biology > 2009 > 390 > 3 > 538-546

Because the rate of a diffusional process such as protein folding is controlled by friction encountered along the reaction pathway, the speed of folding is readily tunable through adjustment of solvent viscosity. The precise relationship between solvent viscosity and the rate of diffusion is complex and even conformation-dependent, however, because both solvent friction and protein internal friction...

article

Kinetics of Folding and Binding of an Intrinsically Disordered Protein: The Inhibitor of Yeast Aspartic Proteinase YPrA

Ranjani Narayanan, Omjoy K. Ganesh, Arthur S. Edison, Stephen J. Hagen

Journal of the American Chemical Society > 2008 > 130 > 34 > 11477 - 11485

article

Kinetics of Internal-Loop Formation in Polypeptide Chains: A Simulation Study

Dana Doucet, Adrian Roitberg, Stephen J. Hagen

Biophysical Journal > 2007 > 92 > 7 > 2281-2289

The speed of simple diffusional motions, such as the formation of loops in the polypeptide chain, places one physical limit on the speed of protein folding. Many experimental studies have explored the kinetics of formation of end-to-end loops in polypeptide chains; however, protein folding more often requires the formation of contacts between interior points on the chain. One expects that, for loops...

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Characterizing the Residue Level Folding of the Intrinsically Unstructured IA ₃ ^†

Omjoy K. Ganesh, Terry B. Green, Arthur S. Edison, Stephen J. Hagen

Biochemistry > 2006 > 45 > 45 > 13585 - 13596

article

Do Protein Molecules Unfold in a Simple Shear Flow?

Juan Jaspe, Stephen J. Hagen

Biophysical Journal > 2006 > 91 > 9 > 3415-3424

Protein molecules typically unfold (denature) when subjected to extremes of heat, cold, pH, solvent composition, or mechanical stress. One might expect that shearing forces induced by a nonuniform fluid flow would also destabilize proteins, as when a protein solution flows rapidly through a narrow channel. However, although the protein literature contains many references to shear denaturation, we...

article

Internal friction in the ultrafast folding of the tryptophan cage

Linlin Qiu, Stephen J. Hagen

Chemical Physics > 2005 > 312 > 1-3 > 327-333

Protein folding is a diffusional process, and the speed of folding is controlled by the frictional forces that act on the polypeptide chain. Several previous studies have suggested that the bulk viscosity of the solvent is the only important source of friction in folding reactions. By contrast, our studies of the folding dynamics of the Tryptophan Cage, a small, ultrafast-folding protein, show clear...

article

Internal friction in the ultrafast folding of the tryptophan cage

Linlin Qiu, Stephen J. Hagen

Chemical Physics > 2004 > 307 > 2-3 > 243-249

Protein folding is a diffusional process, and the speed of folding is controlled by the frictional forces that act on the polypeptide chain. Several previous studies have suggested that the bulk viscosity of the solvent is the only important source of friction in folding reactions. By contrast, our studies of the folding dynamics of the Tryptophan Cage, a small, ultrafast-folding protein, show clear...

article

Internal Friction Controls the Speed of Protein Folding from a Compact Configuration ^†

Suzette A. Pabit, Heinrich Roder, Stephen J. Hagen

Biochemistry > 2004 > 43 > 39 > 12532 - 12538

article

IA ₃ , an Aspartic Proteinase Inhibitor from Saccharomyces cerevisiae , Is Intrinsically Unstructured in Solution ^†

Terry B. Green, Omjoy Ganesh, Kyle Perry, Leif Smith, more

Biochemistry > 2004 > 43 > 14 > 4071 - 4081

article

A Limiting Speed for Protein Folding at Low Solvent Viscosity

Linlin Qiu, Stephen J. Hagen

Journal of the American Chemical Society > 2004 > 126 > 11 > 3398 - 3399

article

Smaller and Faster: The 20-Residue Trp-Cage Protein Folds in 4 μs

Linlin Qiu, Suzette A. Pabit, Adrian E. Roitberg, Stephen J. Hagen

Journal of the American Chemical Society > 2002 > 124 > 44 > 12952 - 12953

INFONA - science communication portal

Search results for: Stephen J. Hagen

Carbohydrate and PepO control bimodality in competence development by Streptococcus mutans

Characterization of LrgAB as a stationary phase-specific pyruvate uptake system in Streptococcus mutans

Co-Assembly Tags Based on Charge Complementarity (CATCH) for Installing Functional Protein Ligands into Supramolecular Biomaterials

Traveling waves in response to a diffusing quorum sensing signal in spatially-extended bacterial colonies

Microfluidic study of competence regulation in Streptococcus mutans: environmental inputs modulate bimodal and unimodal expression of comX

Analysis of gene expression levels in individual bacterial cells without image segmentation

Noise and Crosstalk in the Two Quorum Sensing Channels of Vibrio Fischeri

Noise and crosstalk in two quorum-sensing inputs of Vibrio fischeri

Bacterium in a box: sensing of quorum and environment by the LuxI/LuxR gene regulatory circuit

Solvent Friction Changes the Folding Pathway of the Tryptophan Zipper TZ2

Kinetics of Folding and Binding of an Intrinsically Disordered Protein: The Inhibitor of Yeast Aspartic Proteinase YPrA

Kinetics of Internal-Loop Formation in Polypeptide Chains: A Simulation Study

Characterizing the Residue Level Folding of the Intrinsically Unstructured IA ₃ ^†

Do Protein Molecules Unfold in a Simple Shear Flow?

Internal friction in the ultrafast folding of the tryptophan cage

Internal friction in the ultrafast folding of the tryptophan cage

Internal Friction Controls the Speed of Protein Folding from a Compact Configuration ^†

IA ₃ , an Aspartic Proteinase Inhibitor from Saccharomyces cerevisiae , Is Intrinsically Unstructured in Solution ^†

A Limiting Speed for Protein Folding at Low Solvent Viscosity

Smaller and Faster: The 20-Residue Trp-Cage Protein Folds in 4 μs

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