Structural Analysis of Unsaturated Glycosphingolipids Using Shotgun Ozone-Induced Dissociation Mass Spectrometry

Glycosphingolipids are essential biomolecules widely distributed across biological kingdoms yet remain relatively underexplored owing to both compositional and structural complexity. While the glycan head group has been the subject of most studies, there is paucity of reports on the lipid moiety, particularly the location of unsaturation. In this paper, ozone-induced dissociation mass spectrometry (OzID-MS) implemented in a traveling wave-based quadrupole time-of-flight (Q-ToF) mass spectrometer was applied to study unsaturated glycosphingolipids using shotgun approach. Resulting high resolution mass spectra facilitated the unambiguous identification of diagnostic OzID product ions. Using [M+Na]⁺ adducts of authentic standards, we observed that the long chain base and fatty acyl unsaturation had distinct reactivity with ozone. The reactivity of unsaturation in the fatty acyl chain was about 8-fold higher than that in the long chain base, which enables their straightforward differentiation. Influence of the head group, fatty acyl hydroxylation, and length of fatty acyl chain on the oxidative cleavage of double bonds was also observed. Application of this technique to bovine brain galactocerebrosides revealed co-isolated isobaric and regioisomeric species, which otherwise would be incompletely identified using contemporary collision-induced dissociation (CID) alone. These results highlight the potential of OzID-MS in glycosphingolipids research, which not only provides complementary structural information to existing CID technique but also facilitates de novo structural determination of these complex biomolecules.

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Value sharing problems for differential and difference polynomials of meromorphic functions in a non-Archimedean field

In this paper we discuss the uniqueness problem for differential and difference polynomials of the form (f ^nm (z)f ^nd (qz + c))^(k) for meromorphic functions in a non-Archimedean field.     

On functional equations for meromorphic functions and applications

Donovan’s conjecture states that there exist only finitely many Morita equivalence classes of p-blocks with a given defect. This conjecture was shown by Radha Kessar to be equivalent to two other conjectures, one of which is that the basic algebras of p-blocks with a given defect can all be defined over a single finite field. We shall show that this latter conjecture is equivalent to the seemingly stronger statement that all p-blocks with a given defect can be defined over a single finite field.     

On the Stability and Solution Sensitivity of a Consumer Problem

We present a continuous-time generalization of the seminal research and development model of d’Aspremont and Jacquemin (Am Econ Rev 78(5):1133–1137, 1988) to examine the trade-off between the benefits of allowing firms to cooperate in research and the corresponding increased potential for product market collusion. We show the existence of a solution to the optimal investment problem using a combination of results from viscosity theory and the theory of planar dynamical systems. In particular, we show that there is a critical level of marginal cost at which firms are indifferent between doing nothing and starting to develop the technology. We find that colluding firms develop further a wider range of initial technologies, pursue innovations more quickly, and are less likely to abandon a technology. Product market collusion could thus yield higher total surplus.     

Toll number of the Cartesian and the lexicographic product of graphs

Toll convexity is a variation of the so-called interval convexity. A tolled walk $T$ between two non-adjacent vertices $u$ and $v$ in a graph $G$ is a walk, in which $u$ is adjacent only to the second vertex of $T$ and $v$ is adjacent only to the second-to-last vertex of $T$. A toll interval between $u,v\in V\left(G\right)$ is a set $T_G(u,v)=\{x\in V\left(G\right):x\text{ lies on a tolled walk between }u\text{ and }v\}$. A set $S?V\left(G\right)$ is toll convex, if $T_G(u,v)?S$ for all $u,v\in S$. A toll closure of a set $S?V\left(G\right)$ is the union of toll intervals between all pairs of vertices from $S$. The size of a smallest set $S$ whose toll closure is the whole vertex set is called a toll number of a graph $G$, $tn\left(G\right)$. The first part of the paper reinvestigates the characterization of convex sets in the Cartesian product of two graphs. It is proved that the toll number of the Cartesian product of two graphs equals 2. In the second part, the toll number of the lexicographic product of two graphs is studied. It is shown that if $H$ is not isomorphic to a complete graph, $tn(G°H)\le 3?tn\left(G\right)$. We give some necessary and sufficient conditions for $tn(G°H)=3?tn\left(G\right)$. Moreover, if $G$ has at least two extreme vertices, a complete characterization is given. Furthermore, graphs with $tn(G°H)=2$ are characterized. Finally, the formula for $tn(G°H)$ is given — it is described in terms of the so-called toll-dominating triples or, if $H$ is complete, toll-dominating pairs.     

Comparative analysis of CE‐SSCP to standard RFLP‐CE‐FLA method in quantification of known viral variants within an RNA virus quasispecies

RNA viruses display the highest replication error rate in our biosphere, leading to highly diverse viral populations termed quasispecies. The gold standard method for detection and quantification of variants in a quasispecies is cloning and sequencing, but it is expensive, laborious and time consuming. Therefore, other mutation detection approaches, including SSCP, are often used. In this study, we demonstrate development and the usage of a CE‐SSCP method for quantification of two nearly identical viral variants in heterogenic population of a mumps virus strain and its comparison to RFLP‐CE‐fragment length analysis (RFLP‐CE‐FLA). Analyzed PCR fragments were of the same size (245 bp) with one difference in their nucleotide sequence. The limit of detection of both methods was at 5% of the minor variant. When PCR amplicons of the two variants were pooled, methods' results were very similar. On the contrary, the quantification results of samples in which variants were mixed prior to PCR showed substantial difference between the two methods. Our results indicate that although both methods can be used for detection and monitoring of a specific mutation within a viral population, caution should be taken when quantitative analysis of complex samples is based solely on results of one method.     

Strategies for "wiring" redox-active proteins to electrodes and applications in biosensors, biofuel cells, and nanotechnology

In this tutorial review the basic approaches to establish electrochemical communication between redox-active proteins and electrodes are elucidated and examples for applications in electrochemical biosensors, biofuel cells and nanotechnology are presented. The early stage of protein electrochemistry is described giving a short overview over electron transfer (ET) between electrodes and proteins, followed by a brief introduction into experimental procedures for studying proteins at electrodes and possible applications arising thereof. The article starts with discussing the electrochemistry of cytochrome c, the first redox-active protein, for which direct reversible ET was obtained, under diffusion controlled conditions and after adsorption to electrodes. Next, examples for the electrochemical study of redox enzymes adsorbed on electrodes and modes of immobilization are discussed. Shortly the experimental approach for investigating redox-active proteins adsorbed on electrodes is outlined. Possible applications of redox enzymes in electrochemical biosensors and biofuel cells working by direct ET (DET) and mediated ET (MET) are presented. Furthermore, the reconstitution of redox active proteins at electrodes using molecular wire-like units in order to "wire" the proteins to the electrode surface and possible applications in nanotechnology are discussed.     

Novel route to size-controlled Fe-MIL-88B-NH2 metal-organic framework nanocrystals

A new approach for the synthesis of uniform metal-organic framework (MOF) nanocrystals with controlled sizes and aspect ratios has been developed using simultaneously the non-ionic triblock co-polymer F127 and acetic acid as stabilizing and deprotonating agents, respectively. The alkylene oxide segments of the triblock co-polymer can coordinate with metal ions and stabilize MOF nuclei in the early stage of the formation of MOF nanocrystals. Acetic acid can control the deprotonation of carboxylic linkers during the synthesis and, thus, enables the control of the rate of nucleation, leading to the tailoring of the size and aspect ratio (length/width) of nanocrystals. Fe-MIL-88B-NH(2), as an iron-based MOF crystal, was selected as a typical example to illustrate our approach. The results reveal that this approach is used for not only the synthesis of uniform nanocrystals but also the control of the size and aspect ratio of the materials. The size and aspect ratio of nanocrystals increase with an increase in the concentration of acetic acid in the synthetic mixture. The non-ionic triblock co-polymer F127 and acetic acid can be easily removed from the Fe-MIL-88B-NH(2) nanocrystal products by washing with ethanol, and thus, their amine groups are available for practical applications. The approach is expected to synthesize various nanosized carboxylate-based MOF members, such as MIL-53, MIL-89, MIL-100, and MIL-101.