Devin W Close | University of Utah (original) (raw)

Papers by Devin W Close

Proper gene expression relies on the precise coordination of cellular processes that influence pa... more Proper gene expression relies on the precise coordination of cellular processes that influence packaging, transcription, and processing of the genetic material. Linkage and regulation of these processes is organized by factors that remodel and modify nucleosomes, regulate transcription, and influence RNA processing and export. One of these factors, Spt6, is a large (~168kDa), essential, highly conserved, and functionally diverse eukaryotic protein. Best known as a histone chaperone capable of altering the structure of nucleosomes, Spt6 has also been shown to function as a transcription elongation factor as well as a critical component for proper RNA processing. Although a broader role for Spt6 is reasonably well-understood, very little is known about the functional and mechanistic details of this multifaceted protein. Beyond studying Spt6 directly, insight into Spt6 function may come from complimentary studies on the bacterial protein Tex. Tex is a transcription elongation factor pr...

Journal of Molecular Biology, 2016

We report the engineering of a new reversibly switching chromogenic protein, Dathail. Dathail was... more We report the engineering of a new reversibly switching chromogenic protein, Dathail. Dathail was evolved from the extremely thermostable fluorescent proteins TGP and eCGP123 Kiss et al. (2009), Close and Close (2014) using directed evolution and ratiometric sorting. Dathail has two spectrally distinct chromogenic states with low quantum yields, corresponding to absorbance in a ground state with a maximum at 389 nm, and a photo-induced metastable state with an a maximum at 497 nm.. In contrast to all previously described photoswitchable proteins, both spectral states of Dathail are non-fluorescent. The photo-induced chromogenic state of Dathail has a life-time of ~50 min at 293(o) K and pH 7.5 as measured by UV-Vis spectrophotometry, returning to the ground state through thermal relaxation. X-ray crystallography provided structural insights supporting a change in conformation and coordination in the chromophore pocket as being responsible for Dathail&amp;amp;amp;amp;amp;#39;s photoswitching. Neutron crystallography, carried out for the first time on a protein from the GFP family, showed a distribution of hydrogen atoms revealing protonation of the chromophore 4-hydroxybenzyl group in the ground state. The neutron structure also supports the hypothesis that the photo-induced proton transfer from the chromophore occurs through water mediated proton relay into the bulk solvent. Beyond its spectroscopic curiosity, Dathail has several characteristics that are improvements for applications, including low background fluorescence, large spectral separation, rapid switching time and the ability to switch many times. Therefore, Dathail is likely to be extremely useful in the quickly developing fields of imaging and biosensors, including pcFRET, high resolution microscopy, and live tracking within the cell.

PLOS ONE, 2015

Phanta is a reversibly photoswitching chromoprotein (ΦF, 0.003), useful for pcFRET, that was isol... more Phanta is a reversibly photoswitching chromoprotein (ΦF, 0.003), useful for pcFRET, that was isolated from a mutagenesis screen of the bright green fluorescent eCGP123 (ΦF, 0.8). We have investigated the contribution of substitutions at positions His193, Thr69 and Gln62, individually and in combination, to the optical properties of Phanta. Single amino acid substitutions at position 193 resulted in proteins with very low ΦF, indicating the importance of this position in controlling the fluorescence efficiency of the variant proteins. The substitution Thr69Val in Phanta was important for supressing the formation of a protonated chromophore species observed in some His193 substituted variants, whereas the substitution Gln62Met did not significantly contribute to the useful optical properties of Phanta. X-ray crystal structures for Phanta (2.3 Å), eCGP123T69V (2.0 Å) and eCGP123H193Q (2.2 Å) in their non-photoswitched state were determined, revealing the presence of a cis-coplanar chromophore. We conclude that changes in the hydrogen-bonding network supporting the cis-chromophore, and its contacts with the surrounding protein matrix, are responsible for the low fluorescence emission of eCGP123 variants containing a His193 substitution.

Acta crystallographica. Section D, Biological crystallography, 2014

Microorganisms that degrade biomass produce diverse assortments of carbohydrate-active enzymes an... more Microorganisms that degrade biomass produce diverse assortments of carbohydrate-active enzymes and binding modules. Despite tremendous advances in the genomic sequencing of these organisms, many genes do not have an ascribed function owing to low sequence identity to genes that have been annotated. Consequently, biochemical and structural characterization of genes with unknown function is required to complement the rapidly growing pool of genomic sequencing data. A protein with previously unknown function (Cthe_2159) was recently isolated in a genome-wide screen using phage display to identify cellulose-binding protein domains from the biomass-degrading bacterium Clostridium thermocellum. Here, the crystal structure of Cthe_2159 is presented and it is shown that it is a unique right-handed parallel β-helix protein. Despite very low sequence identity to known β-helix or carbohydrate-active proteins, Cthe_2159 displays structural features that are very similar to those of polysacchari...

Genes & Cancer, 2010

ETS proteins are a family of transcription factors that play important roles in the development o... more ETS proteins are a family of transcription factors that play important roles in the development of cancer. The Ewing's sarcoma EWS/ETS fusion oncoproteins control a number of cancer-relevant phenotypes in that disease. We recently demonstrated that EWS/FLI, the most common EWS/ ETS fusion in Ewing's sarcoma, regulates a portion of its target genes, including the critical target NR0B1, via GGAA-containing microsatellites in their promoters. Given the unusual nature of microsatellites as EWS/FLI response elements, we sought to elucidate the mechanism of EWS/FLI activity at these sites. We found that the ability to bind GGAA microsatellites is shared by multiple ETS family members from distinct phylogenetic subfamilies. Importantly, however, only EWS/ETS-containing fusions are capable of mediating transcriptional activation via these elements, highlighting a neomorphic function of the Ewing's sarcoma fusion proteins. Additional analysis revealed that the GGAA microsatellite binds EWS/FLI with an affinity that is 2 to 3 orders of magnitude lower than previously identified high-affinity consensus/redundant binding sites. The stoichiometry of this interaction is 2 protein molecules for each DNA molecule, suggesting that EWS/FLI binds these elements as a homodimer. The isolated FLI ETS domain bound microsatellite sequences in a nearly identical fashion to full-length EWS/FLI, thus indicating that residues required for homodimeric binding are localized to the ETS domain. These data suggest a new paradigm for an ETS family member binding to DNA at cancer-relevant genetic loci and highlight emergent properties of EWS/FLI that are required for the development of Ewing's sarcoma.

Molecular Cell, 2010

Eukaryotic transcription and mRNA processing depend upon the coordinated interactions of many pro... more Eukaryotic transcription and mRNA processing depend upon the coordinated interactions of many proteins, including Spn1 and Spt6, which are conserved across eukaryotes, are essential for viability, and associate with each other in some of their biologically important contexts. Here we report crystal structures of the Spn1 core alone and in complex with the binding determinant of Spt6. Mutating interface residues greatly diminishes binding in vitro and causes strong phenotypes in vivo, including a defect in maintaining repressive chromatin. Overexpression of Spn1 partially suppresses the defects caused by an spt6 mutation affecting the Spn1 interface, indicating that the Spn1-Spt6 interaction is important for managing chromatin. Spt6 binds nucleosomes directly in vitro, and this interaction is blocked by Spn1, providing further mechanistic insight into the function of the interaction. These data thereby reveal the structural and biochemical bases of molecular interactions that function in the maintenance of chromatin structure.

Microbiology, 2012

Determining transcription factor (TF) recognition motifs or operator sites is central to understa... more Determining transcription factor (TF) recognition motifs or operator sites is central to understanding gene regulation, yet few operators have been characterized. In this study, we used a protein-binding microarray (PBM) to discover the DNA recognition sites and putative regulons for three TetR and one MarR family TFs derived from Burkholderia xenovorans, which are common to the genus Burkholderia. We also describe the development and application of a more streamlined version of the PBM technology that significantly reduced the experimental time. Despite the genus containing many pathogenically important species, only a handful of TF operator sites have been experimentally characterized for Burkholderia to date. Our study provides a significant addition to this knowledge base and illustrates some general challenges of discovering operators on a large scale for prokaryotes.

Journal of Molecular Biology, 2008

Tex is a highly conserved bacterial protein that likely functions in a variety of transcriptional... more Tex is a highly conserved bacterial protein that likely functions in a variety of transcriptional processes. Here we describe two crystal structures of the 86 kDa Tex protein from Pseudomonas aeruginosa at 2.3 Å and 2.5 Å resolution, respectively. These structures reveal a relatively flat and elongated protein, with several potential nucleic-acid binding motifs clustered at one end, including an S1 domain near the C-terminus that displays considerable structural flexibility. Tex binds nucleic acids, with a preference for ssRNA, and the Tex S1 domain is required for this binding activity. Point mutants further demonstrate that the primary nucleic acid binding site corresponds to a surface of the S1 domain. Sequence alignment and modeling indicate that the eukaryotic Spt6 transcription factor adopts a similar core structure. Structural analysis further suggests that the RNA polymerase and nucleosome interacting regions of Spt6 flank opposite sides of the Tex-like scaffold. Therefore, the Tex structure may represent a conserved scaffold that binds ssRNA to regulate transcription in both eukaryotic and prokaryotic organisms.

Journal of Molecular Biology, 2011

The conserved and essential eukaryotic protein Spt6 functions in transcription elongation, chroma... more The conserved and essential eukaryotic protein Spt6 functions in transcription elongation, chromatin maintenance, and RNA processing. Spt6 has three characterized functions. It is a histone chaperone capable of reassembling nucleosomes, a central component of transcription elongation complexes, and is required for recruitment of RNA processing factors to elongating RNA polymerase II (RNAPII). Here, we report crystal structures of the 168 kDa Spt6 protein from Saccharomyces cerevisiae that together represent essentially all of the ordered sequence. Our two structures of the ~900 residue core region reveal a series of putative nucleic acid and proteinprotein interaction domains that fold into an elongated form that resembles the bacterial protein Tex. The similarity to a bacterial transcription factor suggests that the core domain performs nucleosome-independent activities, and as with Tex we find that Spt6 binds DNA. Unlike Tex, however, the Spt6 S1 domain does not contribute to this activity. Crystal structures of the Spt6 Cterminal region reveal a tandem SH2 domain structure comprised of two closely associated SH2 folds. One of these SH2 folds is cryptic, while the other shares striking structural similarity with metazoan SH2 domains and possesses structural features associated with the ability to bind phosphorylated substrates including phosphotyrosine. Binding studies with phosphopeptides that mimic the RNAPII CTD revealed affinities typical of other RNAPII CTD-binding proteins but did not indicate a specific interaction. Overall, these findings provide a structural foundation for understanding how Spt6 encodes several distinct functions within a single polypeptide chain.

BMC Microbiology, 2013

Background: Single cell genomics has revolutionized microbial sequencing, but complete coverage o... more Background: Single cell genomics has revolutionized microbial sequencing, but complete coverage of genomes in complex microbiomes is imperfect due to enormous variation in organismal abundance and amplification bias. Empirical methods that complement rapidly improving bioinformatic tools will improve characterization of microbiomes and facilitate better genome coverage for low abundance microbes.

Biophysical Journal, 2012

Proteins: Structure, Function, and Bioinformatics, 2014

In this paper we describe the engineering and X-ray crystal structure of Thermal Green Protein (T... more In this paper we describe the engineering and X-ray crystal structure of Thermal Green Protein (TGP), an extremely stable, highly soluble, non-aggregating green fluorescent protein. TGP is a soluble variant of the fluorescent protein eCGP123, which despite being highly stable, has proven to be aggregation-prone. The X-ray crystal structure of eCGP123, also determined within the context of this paper, was used to carry out rational surface engineering to improve its solubility, leading to TGP. The approach involved simultaneously eliminating crystal lattice contacts while increasing the overall negative charge of the protein. Despite intentional disruption of lattice contacts and introduction of high entropy glutamate side chains, TGP crystallized readily in a number of different conditions and the X-ray crystal structure of TGP was determined to 1.9 Å resolution. The structural reasons for the enhanced stability of TGP and eCGP123 are discussed.