Long-lived fluorescence of homopolymeric guanine–cytosine DNA duplexes

International audienceThe fluorescence spectrum of the homopolymeric double helix poly(dG)·poly(dC) is dominated by emission decaying on the nanosecond time-scale, as previously reported for the alternating homologue poly(dGdC)·poly(dGdC). Thus, energy trapping over long periods of time is a common feature of GC duplexes which contrast with AT duplexes. The impact of such behaviour on DNA photodamage needs to be evaluated

Optical Properties of Guanine Nanowires: Experimental and Theoretical Study

International audienceLong nanowires formed by ca. 800 guanine tetrads (G4-wires) are studied in phosphate buffer containing sodium cations. Their room temperature optical properties are compared to those of the monomeric chromophore 2-deoxyguanine monophosphate (dGMP). When going from dGMP to G4-wires, both the absorption and the fluorescence spectra change. Moreover, the fluorescence quantum yield increases by a factor of 7.3 whereas the average fluorescence lifetime increases by more than 2 orders of magnitude, indicating emission associated with weakly allowed transitions. The behavior of G4-wires is interpreted in the light of a theoretical study performed in the frame of the exciton theory combining data from molecular dynamics and quantum chemistry. These calculations, carried out for a quadruplex composed of three tetrads, reveal the existence of various exciton states having different energies and oscillator strengths. The degree of delocalization of the quadruplex Franck−Condon excited states is larger than those found for longer duplexes following the same methodology. The slower excited-state relaxation in G4-wires compared to dGMP is explained by emission from exciton states, possibly limited on individual tetrads, whose coherence is reserved by the reduced mobility of guanines due to multiple Hoogsteen hydrogen bonds

Assembling of G-strands into novel tetra-molecular parallel G4-DNA nanostructures using avidin–biotin recognition

We describe a method for the preparation of novel long (hundreds of nanometers), uniform, inter-molecular G4-DNA molecules composed of four parallel G-strands. The only long continuous G4-DNA reported so far are intra-molecular structures made of a single G-strand. To enable a tetra-molecular assembly of the G-strands we developed a novel approach based on avidin–biotin biological recognition. The steps of the G4-DNA production include: (i) Enzymatic synthesis of long poly(dG)-poly(dC) molecules with biotinylated poly(dG)-strand; (ii) Formation of a complex between avidin-tetramer and four biotinylated poly(dG)-poly(dC) molecules; (iii) Separation of the poly(dC) strands from the poly(dG)-strands, which are connected to the avidin; (iv) Assembly of the four G-strands attached to the avidin into tetra-molecular G4-DNA. The average contour length of the formed structures, as measured by AFM, is equal to that of the initial poly(dG)-poly(dC) molecules, suggesting a tetra-molecular mechanism of the G-strands assembly. The height of tetra-molecular G4-nanostructures is larger than that of mono-molecular G4-DNA molecules having similar contour length. The CD spectra of the tetra- and mono-molecular G4-DNA are markedly different, suggesting different structural organization of these two types of molecules. The tetra-molecular G4-DNA nanostructures showed clear electrical polarizability. This suggests that they may be useful for molecular electronics

Serum CEACAM1 Elevation Correlates with Melanoma Progression and Failure to Respond to Adoptive Cell Transfer Immunotherapy

Malignant melanoma is a devastating disease whose incidences are continuously rising. The recently approved antimelanoma therapies carry new hope for metastatic patients for the first time in decades. However, the clinical management of melanoma is severely hampered by the absence of effective screening tools. The expression of the CEACAM1 adhesion molecule on melanoma cells is a strong predictor of poor prognosis. Interestingly, a melanoma-secreted form of CEACAM1 (sCEACAM1) has recently emerged as a potential tumor biomarker. Here we add novel evidences supporting the prognostic role of serum CEACAM1 by using a mice xenograft model of human melanoma and showing a correlation between serum CEACAM1 and tumor burden. Moreover, we demonstrate that serum CEACAM1 is elevated over time in progressive melanoma patients who fail to respond to immunotherapy as opposed to responders and stable disease patients, thus proving a correlation between sCEACAM1, response to treatment, and clinical deterioration

Cation Effect on the Electronic Excited States of Guanine Nanostructures Studied by Time-Resolved Fluorescence Spectroscopy

International audienceThe effect of metal ions on the excited states of guanine nanostructures, short d(TG4T)4 quadruplexes and long G4-wires, are studied by fluorescence spectroscopy. The steadystate emission spectra show that both systems exhibit a strong cation effect. Fluorescence decays and fluorescence anisotropy decays, recorded from the femtosecond to the nanosecond timescale, reveal the following picture. In the presence of K+, emission arises mainly from delocalized ππ* states (excitons), whose decay spans several decades of times. In contrast, the fluorescence in the presence of Na+ is dominated by emission from charge transfer excited states decaying essentially on the subnanosecond time-scale. Such a difference is not due to the initially populated (Franck−Condon) states. The interproton distances derived from two-dimensional NMR measurements on the ground state of d(TG4T)4 show that the geometrical arrangement of guanines, governing the electronic coupling, is the same for both cations, in line with the UV absorption spectra. The observed cation effect is correlated with the excited state relaxation: the increased mobility of Na+ ions within the quadruplex favors trapping of ππ* excitons by charge transfer excited states, whereas such a process is hindered for the larger K+ ions. This is rationalized by quantum calculations on two stacked guanine tetrads

An improved design of optical sensor for long-term measurement of arterial blood flow waveform

We present here the improved design and development of optical sensor for non-invasive measurements of arterial blood flow waveform. The sensor is based on a physical principle of reflective photoplethysmography (PPG). As the light source we used serially connected infrared diodes whereas NPN silicon phototransistors were used as light detectors. The electronic components were molded into square package and poured with silicone. Such preparation produced an elastic superficies that allowed excellent attachment of the sensor on the skins surface. Moreover, a serial connection of infrared diodes and phototransistors completely eliminated signal artifacts caused by minor muscle contractions. The sensor recording performances were examined at the photoplethysmographic sites on three different arteries; the commune carotid, femoral and radial and, on each site the sensor demonstrated remarkable capability to make a consistent, reproducible measurements. Because of the advantageous physical and electrical properties, the new sensor is suitable for various cardiovascular diagnostics procedures, especially when long-term measurements of arterial blood flow waveform are required, for monitoring of different parameters in cardiovascular units and for research