Gnana Prakash Gajula

UV Light Effects on Proteins: From Photochemistry to Nanomedicine

Throughout 4.5 billion year of molecular evolution, proteins have evolved in order to maintain the spatial proximity between aromatic residues (Trp, Tyr and Phe) and disulphide bridges (SS) (Petersen et al, 1999). Aromatic residues are the nanosized antennas in the protein world that can capture UV light (from ~250-298nm). Once excited by UV light they can enter photochemical pathways likely to have harmful effects on protein structures. However, disulphide bridges in proteins are excellent quenchers of the excited state of aromatic residues, contributing this way to protein stability and activity. UV light excitation of the aromatic residues is known to trigger electron ejection from their side chains (Bent & Hayon, 1975a; Bent & Hayon, 1975b; Bent & Hayon, 1975c; Creed, 1984a; Creed, 1984b; Kerwin & Rammele, 2007, Neves-Petersen et al., 2009a). These electrons can be captured by disulphide bridges, leading to the formation of a transient disulphide electron adduct radical, which will dissociate leading to the formation of free thiol groups in the protein. This observation lead to the development in our lab of a new photonic technology, Light Assisted Molecular Immobilization (LAMI), used to functionalize surfaces with biomolecules. This technology is being used in order to create a new generation of biosensors with unsurpassed density (number of spots per mm2). This technology is also being used in order to create nanoparticles based drug delivery systems relevant to nanomedical applications (Parracino et al., 2011).

Photonic Immobilization of BSA for Nanobiomedical Applications: Creation of High Density Microarrays and Superparamagnetic Bioconjugates

Light assisted molecular immobilization has been used for the first time to engineer covalent bioconjugates of superparamagnetic nanoparticles and proteins. The technology involves disulfide bridge disruption upon UV excitation of nearby aromatic residues. The close spatial proximity of aromatic residues and disulfide bridges is a conserved structural feature in proteins. The created thiol groups bind thiol reactive surfaces leading to oriented covalent protein immobilization. We have immobilized a model carrier protein, bovine serum albumin, onto Fe3O4@Au core–shell nanoparticles as well as arrayed it onto optically flat thiol reactive surfaces. This new immobilization technology allows for ultra high dense packing of different bio‐molecules on a surface, allowing the creation of multi‐potent functionalized active new biosensor materials, biomarkers identification and the development of nanoparticles based novel drug delivery system. Bioeng. 2011; 108:999–1010.

Visualization and quantification of four steps in magnetic field induced two-dimensional ordering of superparamagnetic submicron particles

We hereby report a methodology that permits a quantitative investigation of the temporal self-organization of submicron sized superparamagnetic composite particles in the presence of an external magnetic field. The kinetics of field-induced self-organization into linear chains, time-dependent chain-size distribution, resolved growth steps (condensation, polarization, colinearity, and concatenation), the average chain growth rate, and interparticle interaction length were calculated in the presence of a 120 G external magnetic field using optical microscopy and “in-house” developed image analysis software. The measurements are in good agreement with theoretical assumptions.

Modulating the structure of EGFR with UV light: new possibilities in cancer therapy

The epidermal growth factor receptor (EGFR) is a member of the ErbB family of receptor tyrosine kinases. EGFR is activated upon binding to e.g. epidermal growth factor (EGF), leading to cell survival, proliferation and migration. EGFR overactivation is associated with tumor progression. We have previously shown that low dose UVB illumination of cancer cells overexpressing EGFR prior to adding EGF halted the EGFR signaling pathway. We here show that UVB illumination of the extracellular domain of EGFR (sEGFR) induces protein conformational changes, disulphide bridge breakage and formation of tryptophan and tyrosine photoproducts such as dityrosine, N-formylkynurenine and kynurenine. Fluorescence spectroscopy, circular dichroism and thermal studies confirm the occurrence of conformational changes. An immunoassay has confirmed that UVB light induces structural changes in the EGF binding site. A monoclonal antibody which competes with EGF for binding sEGFR was used. We report clear evidence that UVB light induces structural changes in EGFR that impairs the correct binding of an EGFR specific antibody that competes with EGF for binding EGFR, confirming that the 3D structure of the EGFR binding domain suffered conformational changes upon UV illumination. The irradiance used is in the same order of magnitude as the integrated intensity in the solar UVB range. The new photonic technology disables a key receptor and is most likely applicable to the treatment of various types of cancer, alone or in combination with other therapies.

Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues

Fluorescence microscopy is characterized by low background noise, thus a fluorescent object appears as an area of high signal/noise. Thermal gradients may result in apparent motion of the object, leading to a blurred image. Here, we have developed an image processing methodology that may remove/reduce blur significantly for any type of microscopy. A total of ~100 images were acquired with a pixel size of 30 nm. The acquisition time for each image was approximately 1 second. We can quantity the drift in X and Y using the sub pixel accuracy computed centroid location of an image object in each frame. We can measure drifts down to approximately 10 nm in size and a drift-compensated image can therefore be reconstructed on a grid of the same size using the “Shift and Add” approach leading to an image of identical size as the individual image. We have also reconstructed the image using a 3 fold larger grid with a pixel size of 10 nm. The resulting images reveal details at the diffraction limit. In principle we can only compensate for inter-image drift – thus the drift that takes place during the acquisition time for the individual image is not corrected. We believe that our results are of general applicability in microscopy and other types of imaging. A prerequisite for our method is the presence of a trackable object in the image such as a cell nucleus.

Towards Nanoscale Biomedical Devices in Medicine: Biofunctional and Spectroscopic Characterization of Superparamagnetic Nanoparticles

Medical interest in nanotechnology originates from a belief that nanoscale therapeutic devices can be constructed and directed towards its target inside the human body. Such nanodevices can be engineered by coupling superparamagnetic nanoparticle to biomedically active proteins. We hereby report the immobilization of a PhEst, a S-formylglutathione hydrolase from the psychrophilic P. haloplanktis TAC125 onto the gold coated surface of modified superparamagnetic core-shell nanoparticles (Fe3O4@Au). The synthesis of the nanoparticles is also reported. S-formylglutathione hydrolases constitute a family of ubiquitous enzymes which play a key role in formaldehyde detoxification both in prokaryotes and eukaryotes. PhEst was originally annotated as a putative feruloyl esterase, an enzyme that releases ferulic acid (an antioxidant reactive towards free radicals such as reactive oxygen species) from polysaccharides esters. Dynamic light scattering, scanning electron microscopy with energy dispersive X-ray spectroscopy, UV–visible absorption spectroscopy, fluorescence spectroscopy, magnetic separation technique and enzyme catalytic assay confirmed the chemical composition of the gold covered superparamagnetic nanoparticles, the binding and activity of the enzyme onto the nanoparticles. Activity data in U/ml confirmed that the immobilized enzyme is approximately 2 times more active than the free enzyme in solution. Such particles can be directed with external magnetic fields for bio-separation and focused towards a medical target for therapeutical as well as bio-sensor applications.

Photonic cancer therapy: modulating cellular metabolism with light

The epidermal growth factor receptor (EGFR) belongs to the ErbB family of receptor tyrosine kinases. EGFR activation upon binding of ligands (such as EGF and TGF-α) results in cell signaling cascades that promote cell proliferation, survival and apoptosis inhibition. As reported for many solid tumors, EGFR overactivation is associated with tumor development and progression, resistance to cancer therapies and poor prognosis. Therefore, inhibition of EGFR function is a rational cancer therapy approach. We have shown previously that 280 nm UV illumination of two cancer cell lines overexpressing EGFR could prevent phosphorylation of EGFR and of its downstream signalling molecules despite the presence of EGF. Our earlier studies demonstrated that UV illumination of aromatic residues in proteins leads to the disruption of nearby disulphide bridges. Since human EGFR is rich in disulphide bridges and aromatic residues, it is likely that structural changes can be induced upon UV excitation of its pool of aromatic residues (Trp, Tyr and Phe). Such changes may impair the correct binding of ligands to EGFR which will halt the process of tumor growth. In this paper we report structural changes induced by UV light on the extracellular domain of human EGFR. Steady state fluorescence spectroscopy and binding immunoassays were carried out. Our goal is to gain insight at the protein structure level that explains the way the new photonic cancer therapy works. This technology can be applicable to the treatment of various forms of cancer, alone or in combination with other therapies to improve treatment outcome.

Correction: Modulating the Structure of EGFR with UV Light: New Possibilities in Cancer Therapy.

An affiliation for the 6th author is not included. Maria Teresa Neves-Petersen is affiliated with: 2 BioPhotonics Group, Department of Nanomedicine, International Iberian Nanotechnology Laboratory (INL), Braga, Portugal and 6 Department of Clinical Medicine, Aalborg University, Sondre Skovvej 15, 9000 Aalborg, Denmark.

Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues XI

Fluorescence microscopy is characterized by low background noise, thus a fluorescent object appears as an area of high signal/noise. Thermal gradients may result in apparent motion of the object, leading to a blurred image. Here, we have developed an image processing methodology that may remove/reduce blur significantly for any type of microscopy. A total of ~100 images were acquired with a pixel size of 30 nm. The acquisition time for each image was approximately 1 second. We can quantity the drift in X and Y using the sub pixel accuracy computed centroid location of an image object in each frame. We can measure drifts down to approximately 10 nm in size and a drift-compensated image can therefore be reconstructed on a grid of the same size using the “Shift and Add” approach leading to an image of identical size as the individual image. We have also reconstructed the image using a 3 fold larger grid with a pixel size of 10 nm. The resulting images reveal details at the diffraction limit. In principle we can only compensate for inter-image drift – thus the drift that takes place during the acquisition time for the individual image is not corrected. We believe that our results are of general applicability in microscopy and other types of imaging. A prerequisite for our method is the presence of a trackable object in the image such as a cell nucleus.

Image processing for drift compensation in fluorescence microscopy

Fluorescence microscopy is characterized by low background noise, thus a fluorescent object appears as an area of high signal/noise. Thermal gradients may result in apparent motion of the object, leading to a blurred image. Here, we have developed an image processing methodology that may remove/reduce blur significantly for any type of microscopy. A total of ~100 images were acquired with a pixel size of 30 nm. The acquisition time for each image was approximately 1 second. We can quantity the drift in X and Y using the sub pixel accuracy computed centroid location of an image object in each frame. We can measure drifts down to approximately 10 nm in size and a drift-compensated image can therefore be reconstructed on a grid of the same size using the “Shift and Add” approach leading to an image of identical size as the individual image. We have also reconstructed the image using a 3 fold larger grid with a pixel size of 10 nm. The resulting images reveal details at the diffraction limit. In principle we can only compensate for inter-image drift – thus the drift that takes place during the acquisition time for the individual image is not corrected. We believe that our results are of general applicability in microscopy and other types of imaging. A prerequisite for our method is the presence of a trackable object in the image such as a cell nucleus.