Errors in determining coordinates in the digital holography of particles

Based on the approach applied to diffraction-limited optical systems, the study evaluates the measurement errors of transverse and longitudinal coordinates of particle images reconstructed from digital holograms. The paper shows the experimental results of testing the above estimates

Evolutionary changes in the Leishmania eIF4F complex involve variations in the eIF4E–eIF4G interactions

Translation initiation in eukaryotes is mediated by assembly of the eIF4F complex over the m7GTP cap structure at the 5′-end of mRNAs. This requires an interaction between eIF4E and eIF4G, two eIF4F subunits. The Leishmania orthologs of eIF4E are structurally diverged from their higher eukaryote counterparts, since they have evolved to bind the unique trypanosomatid cap-4 structure. Here, we characterize a key eIF4G candidate from Leishmania parasites (LeishIF4G-3) that contains a conserved MIF4G domain. LeishIF4G-3 was found to coelute with the parasite eIF4F subunits from an m7GTP-Sepharose column and to bind directly to LeishIF4E. In higher eukaryotes the eIF4E-eIF4G interaction is based on a conserved peptide signature [Y(X4)Lϕ], where X is any amino acid and Φ is a hydrophobic residue. A parallel eIF4E-binding peptide was identified in LeishIF4G-3 (20-YPGFSLDE-27). However, the binding motif varies extensively: in addition to Y20 and L25, binding strictly requires the presence of F23, whereas the hydrophobic amino acid (Φ) is dispensable. The LeishIF4E–LeishIF4G-3 interaction was also confirmed by nuclear magnetic resonance (NMR) studies. In view of these diversities, the characterization of the parasite eIF4E–eIF4G interaction may not only serve as a novel target for inhibiting Leishmaniasis but also provide important insight for future drug discovery

A novel 4E-interacting protein in Leishmania is involved in stage-specific translation pathways

In eukaryotes, exposure to stress conditions causes a shift from cap-dependent to cap-independent translation. In trypanosomatids, environmental switches are the driving force of a developmental program of gene expression, but it is yet unclear how their translation machinery copes with their constantly changing environment. Trypanosomatids have a unique cap structure (cap-4) and encode four highly diverged paralogs of the cap-binding protein, eIF4E; none were found to genetically complement a yeast mutant failing to express eIF4E. Here we show that in promastigotes, a typical cap-binding complex is anchored through LeishIF4E-4, which associates with components of the cap-binding pre-initiation complex. In axenic amastigotes, expression of LeishIF4E-4 decreases and the protein does not bind the cap, whereas LeishIF4E-1 maintains its expression level and associates with the cap structure and with translation initiation factors. However, LeishIF4E-1 does not interact with eIF4G-like proteins in both life stages, excluding its involvement in cap-dependent translation. Using pull-down assays and mass-spectrometry, we identified a novel, non-conserved 4E-Interacting Protein (Leish4E-IP), which binds to LeishIF4E-1 in promastigotes, but not in amastigotes. Yeast two-hybrid and NMR spectroscopy confirmed the specificity of this interaction. We propose that Leish4E-IP is a translation regulator that is involved in switching between cap-dependent and alternative translation pathways

Multilayer antireflection optical coatings based on Nb, Si and Al oxides for nonlinear ZnGeP2 crystals

The effect of the designed antireflection coatings based on Nb2O5/Al2O3 and Nb2O5/SiO2 pairs of materials on the laser-induced damage threshold (LIDT) of ZnGeP2 crystals at a wavelength of 2097 nm is shown. The coating was applied using the ion-beam sputtering (IBS) method. The LIDT of the sample coated with Nb2O5/SiO2 was W0d = 1.8 J/cm2. The LIDT of a sample coated with Nb2O5/Al2O3 is W0d = 2.35 J/cm2. The presence of silicon conglomerates in the antireflection coating leads to a decrease the LIDT of a nonlinear crystal due to local thermomechanical stresses and scattering of the incident laser radiation

Visualization of volumetric defects and dynamic processes in crystals by digital IR holography

In this work, the method of IR digital holography intended for detection of volumetric defects in ZnGeP2 single crystals has been tested. A method of visualization of the process of optical damage of a ZnGeP2 single crystal using digital holography is suggested

Accuracy of determination of longitudinal coordinates of particles by digital holography

Based on known expressions applied to diffraction-limited optics systems, estimates are given and a technique is suggested for determining the measurement error in the longitudinal coordinates of particles from images reconstructed from digital holograms. A correction factor for visual focusing is determined for different distances between a detected particle and the plane of a CMOS array. The results of experimental tests of the technique are presented. A possibility is shown of reducing the error of automatic digital focusing by means of simultaneous use of focusing curves for several quality indicators and optimization of the image area for their constructio

Structural basis for LeishIF4E-1 modulation by an interacting protein in the human parasite Leishmania major

Abstract Leishmania parasites are unicellular pathogens that are transmitted to humans through the bite of infected sandflies. Most of the regulation of their gene expression occurs post-transcriptionally, and the different patterns of gene expression required throughout the parasites’ life cycle are regulated at the level of translation. Here, we report the X-ray crystal structure of the Leishmania cap-binding isoform 1, LeishIF4E-1, bound to a protein fragment of previously unknown function, Leish4E-IP1, that binds tightly to LeishIF4E-1. The molecular structure, coupled to NMR spectroscopy experiments and in vitro cap-binding assays, reveal that Leish4E-IP1 allosterically destabilizes the binding of LeishIF4E-1 to the 5′ mRNA cap. We propose mechanisms through which Leish4E-IP1-mediated LeishIF4E-1 inhibition could regulate translation initiation in the human parasite

Application of infrared digital holography for characterization of inhomogeneities and voluminous defects of single crystals on the example of ZnGeP2

In this work, the method of IR digital holography intended for detection of volumetri