Research Interests

Research of Dr. Turner's Laboratory falls into a number of different areas: Protein Chemistry, Microbiology biochemistry, Biochemistry, Biophysical chemistry, Structural Biology, Molecular Microbiology, Bioinformatics, Environmental biogeochemistry and bioinorganic chemistry.

For a list of our groups technical expertise, protocols, and instrumentation see our Methods page.

There are two major focuses of the Turner laboratory

1) The study of the targeting, folding, structure, and assembly of integral membrane proteins. Under this umbrella several research projects are underway.

• We are investigating the phenotypes, folding and structure of members of the Small Multidrug Resistance (SMR) protein family. We are using the biophysical techniques of fluorescence, calorimetry, FT-IR, stop-flow methods, and size-exclusion HPLC to examine the SMR proteins structure and ligand binding properties in various biomembrane mimetic environments. Additionally, we are investigating the molecular microbiology phenotypes of the Sug subclass of the SMR proteins.

• Protein targeting to the Tat protein translocon is under investigation. Our group has identified a twin-arginine leader binding protein and other redox enzyme maturation proteins (REMPs) that behave as specific proofreading chaperones that escort various oxido-reductases to this translocase. We are using biochemical and proteomic approaches to characterization of these chaperones involved in this translocation pathway.

• Fluorescence spectroscopy of proteins is our laboratories specialized technique. Research into the photochemistry of the amino acid tryptophan to change its spectroscopic properties is underway. This research is focused on developing unique spectroscopic probes useful to the study of protein structure and function, particularly that of integral membrane proteins.

2) Environmental Microbiology.

• The mechanisms of bacterial resistance towards the metalloid oxyanion tellurite (TeO₃^2-). The metabolism, biochemistry and chemistry of this oxyanion in E. coli is the present primary focus.

• Exposure of bacterial biofilms to metals. Here we are studying resistance mechanisms, physiology changes, and biogeochemical processes.

Department of Biological Sciences Web site link for Dr. R.J. Turner.

Biographical Sketch of Dr. Turner

For those interest in graduate studies or postdoctoral work in the laboratory of Dr. Turner, check out available positions.

Dr. Turners research program at the University of Calgary was initiated with an AHFMR establishment grant. The research in the group is funded by NSERC and CIHR operating grants. Additionally, considerable success with equipment grants has also provided an excellent research environment for the Turner research team.

Project Descriptions

Also see Turner laboratory Publications

Small Multidrug Resistance Proteins
The Small Multidrug Resistance (SMR) family of proteins in bacteria are presently being investigated with a focus to understand structure and function relationships.  These proteins have an activity of in efflux of toxic quaternary ammonium compounds, antiseptics and DNA intercalating dyes.   SMR proteins contain on the order of 110 amino acids and are predicted to contain 4 transmembrane helices. The SMR protein family is composed of two groups based on sequence similarity. The Smp group (small multidrug pumps) are proton antiporters and catalyze the efflux of a variety of toxic compounds. The Sug group, although 60% similar and 35% identical to the Smp group show no observable QAC resistance or efflux. 

We are studying the biochemistry and microbiology of the SMR proteins as well as using them as a tool to study membrane protein folding. We have explored the multimeric forms by SEC-HPLC. The ligand binding of the EmrE is being explored by isothermal titration calorimetry and fluorescence spectroscopy. We have also explored the folding of EmrE in various membrane mimetic environments. Our research will continue to explore these aspects of EmrE and other SMR proteins.

    We have used sequence similarities to identify key amino acid residues that may be responsible for the differences between the Smp proteins and the Sug proteins.  Using site-directed mutagenesis we are determining using a directed evolution approach what it takes to make a Smp.  We are also using a variety of classical microbiology and molecular biology approaches to identify the function of the Sug proteins.

Assembly and Targeting of Multimeric Oxidoreductases.
    A novel protein translocation mechanism has been discovered (Weiner et al., 1998).  The working idea of this Sec-independent translocase is that the proteins are transported across the membrane in a 'folded-state'.  The leader sequence of proteins that utilize this translocase contain a "twin-arginine motif.    We have studied the twin-arginine leader of dimethyl sulfoxide reductase and its role in targeting and assembly of the trimeric enzyme (Sambasivarao et al., 2000).  As other competitor groups have concentrated their efforts on understanding the translocon itself, our group has concentrated on identifying other proteins that are involved in the translocation mechanism.

   The present goal of Dr. Turner's research on this system is focusing on identifying twin-arginine leader binding proteins.   Our hypothesis is that there must be chaperones and/or specific escort proteins to aid in targeting the twin-arginine leader containing proteins to the translocase. In 2001 we discovered a twin-arginine leader binding protein that was subsequently termed DmsD that interacts with the leader of DmsA (the catalytic subunit of DMSO reductase) (Oresnik et al., 2001). Through Bioinformatic analysis in collaboration with Dr. Frank Sargent we have identified a group of proteins defined as Redox Enzyme Maturation Proteins (REMPs).

We have been studying the protein chemistry of the REMP chaperone DmsD. We have explored the multimeric and folding forms. We are also interested in ligand binding to this protein and other REMPs. The nature of the biochemical features of the targeting leader and its interactions with the REMP are under investigation.

Another important question to be asked about the Tat translocon system is the pathway from the ribosome to the Tat translocase. We are interested in this pathway and all the proteins involved. Using protein-protein interaction approaches we are examining the interactome of the REMP’s.

The mode of translocon membrane pore formation is an interesting question of this system. We are using both computation methods in collaboration with Dr. Peter. Tieleman and membrane protein structure methods to expore such questions.

Environmental Microbiology; Metal Resistance in Bacteria.
    An interest in heavy metal processing by bacteria stems back over 10 years.  The main focus has been the resistance and toxicity of oxyanions of tellurium.  The focus has been to understand the mechanisms of bacterial resistance to tellurite.  Research to date has determined that the identified resistance determinants encoded are unique compared to that of other heavy metal resistance mechanisms. Considerable effort has been spent on examining the metabolism of tellurite in E. coli in order to determine the mode of toxicity.  Although there are a lot of similarities in the chemistry between selenium and tellurium, the chemical properties of the different forms can be quite different.  It is through such studies we hope to understand why tellurium oxyanions are 100-1000 fold more toxic than selenium oxyanions.
    The tehAtehB determinant is a cryptic resistance determinant found on the chromosome of a number of enteric bacteria.  This is one of the only determinants that appears to have only one phenotype, that of resistance to tellurite.  Therefore we have concentrated the majority of our effort on this determinant.  Recent research has identified that TehB is a tellurite - S-adenosine methionine binding protein (Liu et al., 2000; Dyllick-Brenzinger et al., 2000).   This protein apparently acts as a dimer and involves cysteine residues for mediating full resistance.  Additionally, evidence suggests that TehA (and integral membrane protein) has the ability to act as a transporter (Turner et al., 1997).   We continue to link together such clues and hope to get a complete picture of this determinants mechanism.    

We have recently been exploring metal resistance in bacterial biofilms. As apposed to biofilms resistance to antibiotics, biofilms do not demonstrate the same resistance to heavy metal antimicrobials (Harrison et al., 2004). It is apparent that the metal processing is different in bacteria growing in the planktonic versus biofilm state.

Fluorescence Spectroscopy
    The major biophysical technique at our disposal for studying protein folding and function is fluorescence spectroscopy.  As fluorescence is very sensitive technique to monitor changes in probe dynamics and environment, it is an ideal tool for the study of membrane proteins.  Our fluorometer is interfaced with a Stop-Flow cell allowing for kinetic analysis of membrane protein folding and assembly in the microsec to min time scales.  Examining changes in fluorescence parameters of intensity and wavelength as well as methods of Quenching, Anisotropy (Polarization) and Försters Resonance Energy Transfer (FRET) are beginning to be employed in studying the SMR family of proteins.
    In addition to using fluorescence to study membrane proteins we are also interested in the use of this system to study protein-protein interactions and ligand binding.
    We are also spending time investigating the fluorescence properties of various chemically modified forms of tryptophan as potential tools as probes for proteins. We have characterized the exited-state chemistry of haloalkane reactions with the indol side chain of tryptophan (Edwards et al., 2002). The result is close to a 150 nm red shift in the spectroscopic signature. In collaboration with Dr. Rob Edwards we are characterizing this chemistry and the spectrophysics of the products.

Recently we have obtained a frequency domain time-resolved fluorometer. We will utilize this spectrometer to study the photophysics of the haloalkane indol chemistry as well as integral membrane protein folding and ligand binding.

Prediction of Folding and Interaction of Helices of Integral Membrane Proteins
    In collaboration with Dr. Rob Edwards we are have been using multiple sequence alignment information in conjunction with hydropathy analysis to predict the topology of anchor subunits of multimeric proteins.  Additionally, using such information, transmembrane helices can be accurately predicted and helices can be separated into buried and lipid exposed.  Furthermore the face of the helix interacting with the lipids can also be predicted with good reliability. Understanding the geometric interactions of helices in integral membrane proteins is the next step towards prediction of the tertiary structure and understanding how such proteins carry out their biochemical roles in the cell.