Elka R Georgieva

Texas Tech University | TTU · Department of Chemistry and Biochemistry

Sodium and aspartate symporter from Pyrococcus horikoshii, Glt(Ph), is a homolog of the mammalian glutamate transporters, homotrimeric integral membrane proteins that control neurotransmitter levels in brain synapses. These transporters function by alternating between outward-facing and inward-facing states, in which the substrate binding site is o...

Integral membrane proteins (IMPs) fulfill important physiological functions by providing cell–environment, cell–cell and virus–host communication; nutrients intake; export of toxic compounds out of cells; and more. However, some IMPs have obliterated functions due to polypeptide mutations, modifications in membrane properties and/or other environme...

We report our findings on the assembly of the HIV-1 protein Vpu into soluble oligomers. Vpu is a key HIV-1 protein. It has been considered exclusively a single-pass membrane protein. Previous observations show that this protein forms stable oligomers in aqueous solution, but details about these oligomers still remain obscure. This is an interesting...

Mycobacterium tuberculosis (Mtb) drug exporters contribute an efficient mechanism for drug resistance. Therefore, understanding the structure/function relationship in these proteins is important. We focused on the Mtb EfpA efflux pump, which belongs to the major facilitator superfamily (MSF) and transports anti-tuberculosis drugs outside the bacter...

The HIV-1-encoded protein Vpu forms an oligomeric ion channel/pore in membranes and interacts with host proteins to support the virus lifecycle. However, Vpu molecular mechanisms are currently not well understood. Here, we report on the Vpu oligomeric organization under membrane and aqueous conditions and provide insights into how the Vpu environme...

To delve into the structure–function relationship of transmembrane proteins (TMPs), robust protocols are needed to produce them in a pure, stable, and functional state. Among all hosts that express heterologous TMPs, E. coli has the lowest cost and fastest turnover. However, many of the TMPs expressed in E. coli are misfolded. Several strategies ha...

To delve into the structure-function relationship of transmembrane proteins (TMPs), robust protocols are needed to produce them in a pure, stable, and functional state. Among all hosts that express heterologous TMPs, E. coli has the lowest cost and fastest turnover. However, many of the expressed in E. coli TMPs are misfolded. Several strategies ha...

We compared the conformations of the transmembrane domain (TMD) of influenza A M2 (IAM2) protein reconstituted at pH 7.4 in DOPC/DOPS bilayers to those in isolated E. coli membranes, having preserved its native proteins and lipids. IAM2 is a single-pass transmembrane protein known to assemble into homo-tetrameric proton channel. To represent this c...

We study the structure of the HIV-1 encoded protein Vpu, which fulfils important roles for the virus functions. To date, Vpu has been considered exclusively a single-pass membrane protein. However, our studies revealed that this protein forms stable oligomers in aqueous solution with currently unknown physiological role. Therefore, the detailed cha...

The HIV-1 encoded protein Vpu forms an oligomeric ion channel/pore in membranes and interacts with multiple host proteins to support virus lifecycle. However, Vpu molecular mechanisms are currently not well understood. The structures of full-length Vpu in its monomeric and oligomeric forms are unknown, although both the monomer and oligomer are dee...

We investigate the molecular mechanisms of the Mycobacterium tuberculosis (Mtb) EfpA membrane exporter. EfpA is a ca. 56 kDa monomeric integral membrane protein, which belongs to the Major Facilitator Superfamily transporters, and the QacA subfamily. It has fourteen predicted transmembrane segments/helices (TMs) with both N-and C-termini located in...

We study the structure and function of small viral membrane proteins, which are expressed in the host and function in cellular membranes. Typically, they are multi-domain multi-functional proteins aiding virus adaptation and proliferation. Detailed characterization of the structure-function relationship of these proteins will help to better underst...

Detailed study of conformational rearrangements and dynamics of proteins is central to our understanding of their physiological functions and the loss of function. This review outlines the applications of the electron paramagnetic resonance (EPR) technique to study the structural aspects of proteins transitioning from a solution environment to the...

Mycobacterium tuberculosis ( Mtb ) causes the very severe disease tuberculosis. To fight Mtb infection, detailed understanding of the pathogen molecular mechanisms in the host is needed. To this end, comprehensive knowledge about Mtb membrane transport system, which is currently not well researched, is a high priority. Our focus is on the Mtb ‐enco...

Human T-cell leukemia virus type 1 is an oncovirus that causes aggressive adult T-cell leukemia but is also responsible for severe neurodegenerative and endocrine disorders. Combatting HTLV-1 infections requires a detailed understanding of the viral mechanisms in the host. Therefore, in vitro studies of important virus-encoded proteins would be cri...

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of illnesses, such as adult T-cell leukemia/lymphoma, myelopathy/tropical spastic paraparesis (a neurodegenerative disorder), and other diseases. Therefore, HTLV-1 infection is a serious public health concern. Currently, diseases caused by HTLV-1 cannot be prevented or cured. Hence,...

Membrane proteins such as ion channels and transporters are frequently homomeric. The homomeric nature raises important questions regarding coupling between subunits and complicates the application of techniques such as FRET or DEER spectroscopy. These challenges can be overcome if the subunits of a homomeric protein can be independently modified f...

Viral fusogens merge viral and cell membranes during cell penetration. Their ectodomains drive fusion by undergoing large-scale refolding, but little is known about the functionally important regions located within or near the membrane. Here we report the crystal structure of full-length glycoprotein B (gB), the fusogen from herpes simplex virus, c...

The self-assembly of the microtubule associated tau protein into fibrillar cell inclusions is linked to a number of devastating neurodegenerative disorders collectively known as tauopathies. The mechanism by which tau self-assembles into pathological entities is a matter of much debate, largely due to the lack of direct experimental insights into t...

We adapt a new wavelet-transform-based method of denoising experimental signals to pulse-dipolar electron-spin resonance spectroscopy (PDS). We show that signal averaging times of the time-domain signals can be reduced by as much as 2 orders of magnitude, while retaining the fidelity of the underlying signals, in comparison with noiseless reference...

All enveloped viruses must catalyze the fusion of their surrounding membrane with that of their target cell. In herpesviruses, fusion is powered by a large structural rearrangement of the trimeric fusogen gB, with help from viral glycoproteins gD and gH/gL. Although the structure of the postfusion gB ectodomain has been solved, the architecture of...

Cellular membranes and associated proteins play critical physiological roles in organisms of all life kingdoms. In many cases malfunction of biological membranes triggered by changes in the lipid bilayer properties or membrane protein functional abnormalities lead to severe diseases. In order to understand in detail the processes that govern life o...

The M2 protein from influenza A plays important roles in its viral cycle. It contains a single transmembrane helix, which oligomerizes into a homotetrameric proton channel that conducts in the low-pH environment of the host-cell endosome and Golgi apparatus, leading to virion uncoating at an early stage of infection. We studied conformational rearr...

The M2 proton channel is essential to the influenza a virus life cycle. This single-pass helical membrane protein, which assembles in a tetramer, is a target for anti-influenza pharmacological development. The study of M2 is critical to our understanding of the mechanisms by which drugs inhibit its function and is also important in the more general...

Cyclooxygenases (COX) are heme containing sequence homodimers that utilize tyrosyl radical-based catalysis to oxygenate substrates. Tyrosyl radicals are formed from a single turnover of substrate in the peroxidase active site generating an oxy-ferryl porphyrin cation radical intermediate that subsequently gives rise to a Tyr-385 radical in the cycl...

M2 from influenza A virus functions as an oligomeric proton channel essential for the viral cycle, hence it is a high-priority pharmacological target whose structure and functions require better understanding. We studied the mechanism of M2 transmembrane domain (M2TMD) assembly in lipid membranes by the powerful biophysical technique of double elec...

Influenza A M2 is a single‐pass transmembrane protein, that assembles into tetrameric proton channels. This protein is a pharmacological target and knowing its structural and functional properties is of high importance. We studied the assembly of M2 transmembrane domain of (M2TMD) in DOPC/POPS membranes. To this end, we employed one of the modaliti...

Glutamate transporters terminate neurotransmission by clearing synaptically released glutamate from the extracellular space, allowing repeated rounds of signalling and preventing glutamate-mediated excitotoxicity. Crystallographic studies of a glutamate transporter homologue from the archaeon Pyrococcus horikoshii, GltPh, showed that distinct trans...

Tau is a microtubule-associated protein that is genetically linked to dementia and linked to Alzheimer's disease via its presence in intraneuronal neurofibrillary tangle deposits, where it takes the form of aggregated paired helical and straight filaments. Although the precise mechanisms by which tau contributes to neurodegeneration remain unclear,...

The influenza A M2 protein is single-pass transmembrane protein that assembles in a tetramer, forming a pH-activated proton channel. It is essential for viral function. The tetramer of M2 transmembrane domain (M2TM), residues 22-46, is the minimal unit for proton conductance. Although substantial knowledge about M2-membrane interactions was accumul...

We describe significantly improved long-distance measurements in biomolecules by use of the new multipulse double electron-electron spin resonance (DEER) illustrated with the example of a five-pulse DEER sequence. In this sequence, an extra pulse at the pump frequency is used compared with standard four-pulse DEER. The position of the extra pulse i...

P-glycoprotein (Pgp, ABCB1) is an ABC transporter that uses the energy of ATP hydrolysis to efflux a variety of amphipathic substrates including anti-cancer agents from the cell. In this study, we have used disulfide crosslinking and Pulsed Dipolar Electron Spin Resonance Spectroscopy (PDS) to elucidate the conformational changes associated with th...

Alpha-synuclein (alphaS) is linked to Parkinson disease through its deposition in an amyloid fibril form within Lewy Body deposits, and by the existence of three alphaS point mutations that lead to early onset autosomal dominant Parkinsonism. The normal function of alphaS is thought to be linked to the ability of the protein to bind to the surface...

We apply pulsed dipolar ESR spectroscopy (Ku-band DEER) to elucidate the global conformation of the Parkinson's disease-associated protein, alpha-synuclein (alphaS) bound to small unilamellar phospholipid vesicles, rodlike SDS micelles, or lipid bicelles. By measuring distances as long as approximately 7 nm between introduced pairs of nitroxide spi...

The structural properties of Mycobacterium tuberculosis (Mtb) ribonucleotide reductase R2 protein were studied under varying pH and temperature conditions by circular dichroism (CD) spectroscopy as well as dynamic light scattering (DLS). Under physiological conditions this protein has a high alpha-helical content, similar to the corresponding prote...

The EPR spectrum of sucrose irradiated by high-energy radiation is complex due to the presence of more than one radical species. In order to decompose the spectrum and elucidate the radical magnetic parameters a high-field (HF(-)EPR) study on stable free radicals in gamma-irradiated polycrystalline sucrose (table sugar) was performed at three diffe...

The EPR and UV spectral properties of gamma-irradiated white and burned sugar, fructose and glucose are studied with the accent on their suitability as dosimetric materials. It is shown that gamma-irradiation of solid samples of white sugar and fructose yields stable EPR spectra whereas glucose signal remains time-dependent even 11 months later. Su...

The possibilities for the estimation of the absorbed dose for high-energy radiation with a new self-calibrated dosimeter containing table sugar as a radiation-sensitive material and Mn2+/MgO as an internal standard by the method of electron paramagnetic resonance (EPR) is reported. The dose response of this dosimeter is represented as the ratio bet...