Effect of pressure on islet amyloid polypeptide aggregation: revealing the polymorphic nature of the fibrillation process

Type II diabetes mellitus is a disease which is characterized by peripheral insulin resistance coupled with a progressive loss of insulin secretion that is associated with a decrease in pancreatic islet beta-cell mass and the deposition of amyloid in the extracellular matrix of beta-cells, which lead to islet cell death. The principal component of the islet amyloid is a pancreatic hormone called islet amyloid polypeptide (IAPP). High-pressure coupled with FT-IR spectroscopic and AFM studies were carried out to elucidate further information about the aggregation pathway as well as the aggregate structures of IAPP. To this end, a comparative fibrillation study of IAPP fragments was carried out as well. As high hydrostatic pressure (HHP) is acting to weaken or even prevent hydrophobic self-organization and electrostatic interactions, application of HHP has been used as a measure to reveal the importance of these interactions in the fibrillation process of IAPP and its fragments. IAPP preformed fibrils exhibit a strong polymorphism with heterogeneous structures, a large population of which are rather sensitive to high hydrostatic pressure, thus indicating a high percentage of ionic and hydrophobic interactions and loose packing of these species. Conversely, fragments 1-19 and 1-29 are resistant to pressure treatment, suggesting more densely packed aggregate structures with less void volume and strong cooperative hydrogen bonding. Furthermore, the FT-IR data indicate that fragment 1-29 has intermolecular beta-sheet conformational properties different from those of fragment 1-19, the latter exhibiting polymorphic behavior with more disordered structures and less strongly hydrogen bonded fibrillar assemblies. The data also suggest that hydrophobic interactions and/or less efficient packing of amino acids 30-37 region leads to the marked pressure sensitivity observed for full-length IAPP.     

Multistep Photoluminescence Decay Reveals Dissociation of Geminate Charge Pairs in Organolead Trihalide Perovskites

Charge carrier dynamics in organolead iodide perovskites is analyzed by employing time‐resolved photoluminescence spectroscopy with several ps time resolution. The measurements performed by varying photoexcitation intensity over five orders of magnitude enable separation of photoluminescence components related to geminate and nongeminate charge carrier recombination and to address the dynamics of an isolated geminate electron–hole pair. Geminate recombination dominates at low excitation fluence and determines the initial photoluminescence decay. This decay component is remarkably independent of the material structure and experimental conditions. It is demonstrated that dependences of the geminate and nongeminate radiative recombination components on excitation intensity, repetition rate, and temperature, are hardly compatible with carrier trapping and exciton dissociation models. On the basis of semiclassical and quantum mechanical numerical calculation results, it is argued that the fast photoluminescence decay originates from gradual spatial separation of photogenerated weakly bound geminate charge pairs.     

Flavone Derivatives as Inhibitors of Insulin Amyloid-Like Fibril Formation

Several natural and synthetic flavone derivatives have been reported to inhibit formation of amyloid fibrils or to remodel existing fibrils. These studies suggest that the numbers and positions of hydroxyl groups on the flavone rings determine their effectiveness as amyloid inhibitors. In many studies the primary method for determining the effectiveness of inhibition is measuring Thioflavin T (ThT) fluorescence. This method demonstrably results in a number of false positives for inhibition. We studied the effects of 265 commercially available flavone derivatives on insulin fibril formation. We enhanced the effectiveness of ThT fluorescence measurements by fitting kinetic curves to obtain halftime of aggregation (t ₅₀). Maximal values of ThT fluorescence varied two fold or more in one third of all cases, but this did not correlate with changes in t ₅₀. Changes in t ₅₀ values were more accurate measures of inhibition of amyloid formation. We showed that without a change in an assay, but just by observing complete kinetic curves it is possible to eliminate numbers of false positive and sometimes even false negative results. Examining the data from all 265 flavones we confirmed previous observations that identified the importance of hydroxyl groups for inhibition. Our evidence suggests the importance of hydroxyl groups at locations 5, 6, 7, and 4’, and the absence of a hydroxyl group at location 3, for inhibiting amyloid formation. However, the main conclusion is that the positions are not additive. The structures and their effects must be thought of in the context of the whole molecule.     

Effects of tunable excitation in carotenoids explained by the vibrational energy relaxation approach

Carotenoids are fundamental building blocks of natural light harvesters with convoluted and ultrafast energy deactivation networks. In order to disentangle such complex relaxation dynamics, several studies focused on transient absorption measurements and their dependence on the pump wavelength. However, such findings are inconclusive and sometimes contradictory. In this study, we compare internal conversion dynamics in \(\beta\)-carotene, pumped at the first, second, and third vibronic progression peak. Instead of employing data fitting algorithms based on global analysis of the transient absorption spectra, we apply a fully quantum mechanical model to treat the high-frequency symmetric carbon–carbon (C=C and C–C) stretching modes explicitly. This model successfully describes observed population dynamics as well as spectral line shapes in their time-dependence and allows us to reach two conclusions: Firstly, the broadening of the induced absorption upon excess excitation is an effect of vibrational cooling in the first excited state (\(S_{1}\)). Secondly, the internal conversion rate between the second excited state (\(S_{2}\)) and \(S_{1}\) crucially depends on the relative curve displacement. The latter point serves as a new perspective on solvent- and excitation wavelength-dependent experiments and lifts contradictions between several studies found in literature.     

Recombinant chromosome 14 due to maternal pericentric inversion

Chromosome 14 is often involved in various chromosome rearrangements, most of them balanced. Human chromosome 14 is acrocentric, so its pericentric inversions are extremely rare (only few cases have been described in the literature). Here we report on a boy with congenital malformations and recombinant chromosome 14 inherited from his mother carrying a pericentric inversion. The proband's G-banded chromosome analysis revealed derivative chromosome 14. Comparative genomic hybridization analysis identified duplication of the terminal part of chromosome 14q ish cgh dup(14)(q32.1qter). This abnormality has been confirmed by custom BAC FISH analysis. His mother's karyotype was 46,XX,inv(14)(p11.2q32.1).     

1H, 13C and 15N resonance assignments of the major extracytoplasmic domain of the cell shape-determining protein MreC from Bacillus subtilis

MreB, MreC and MreD are essential cell shape-determining morphogenetic proteins in Gram-positive and in Gram-negative bacteria. While MreB, the bacterial homologue of the eukaryotic cytoskeletal protein actin, has been extensively studied, the roles of MreC and MreD are less well understood. They both are transmembrane proteins. MreC has a predicted single transmembrane domain and the C-terminal part outside the cell membrane. MreC probably functions as a link between the intracellular cytoskeleton and the cell wall synthesizing machinery which is located at the outer surface of the cell membrane. Also proteins involved in cell wall synthesis participate in cell morphogenesis. How these two processes are coordinated is, however, poorly understood. Bacillus subtilis (BS), a non-pathogenic Gram-positive bacterium, is widely used as a model for Gram-positive pathogens, e.g. Staphylococcus aureus (SA). Currently, the structures of MreC from BS and SA are not known. As part of our efforts to elucidate the structure–function relationships of the morphogenetic protein complexes in Gram-positive bacteria, we present the backbone and side chain resonance assignments of the extracytoplasmic domain of MreC from BS.     

Pyrrolidinone-bearing methylated and halogenated benzenesulfonamides as inhibitors of carbonic anhydrases

Two series of benzenesulfonamides bearing methyl groups at ortho/ortho or meta/ortho positions and a pyrrolidinone moiety at para position were synthesized and tested as inhibitors of the twelve catalytically active human carbonic anhydrase (CA) isoforms. Observed binding affinities were determined by fluorescent thermal shift assay and intrinsic binding affinities representing the binding of benzenesulfonamide anion to the Zn(II)-bound water form of CA were calculated. Introduction of dimethyl groups into benzenesulfonamide ring decreased the binding affinity to almost all CA isoforms, but gained in selectivity towards one CA isoform. A chloro group at the meta position of 2,6-dimethylbenzenesulfonamide derivatives did not influence the binding to CA I, but it increased the affinity to all other CAs, especially, CA VII and CA XIII (up to 500 fold). The compounds may be used for further development of CA inhibitors with higher selectivity to particular CA isoforms.     

Genome of Klebsiella sp.-infecting bacteriophage vB_KleM_RaK2

Despite the fact that multidrug-resistant Klebsiella sp. strains emerge rapidly (Xu J, et al., Adv. Mater. Res. 268-270:1954-1956, 2011) and bacteriophages have been reported to be useful in controlling these bacteria (Kumari S, Harjai K, Chhibber S, J. Med. Microbiol. 60:205-210, 2011), the complete genome sequences of only five Klebsiella phages (four siphoviruses and one myovirus) can be found in databases. In this paper, we report on the complete genome sequence of Klebsiella sp.-infecting bacteriophage vB_KleM_RaK2. With a genome size of 345,809 bp, this is the second largest myovirus and the largest Klebsiella phage sequenced to date. This phage differs substantially from other myoviruses since 411 out of 534 vB_KleM_RaK2 open reading frames have no known functions and lack any reliable database matches. Comparative analysis of the genome sequence of vB_KleM_RaK2 suggests that this phage forms a distinct phylogenetic branch within the family Myoviridae of tailed bacteriophages.