Daniel Persson

Uptake of analogs of penetratin, Tat(48-60) and oligoarginine in live cells.

Cell-penetrating peptides are regarded as promising vectors for intracellular delivery of large, hydrophilic molecules, but their mechanism of uptake is poorly understood. Since it has now been demonstrated that the use of cell fixation leads to artifacts in microscopy studies on the cellular uptake of such peptides, much of what has been considered as established facts must be reinvestigated using live (unfixed) cells. In this work, the uptake of analogs of penetratin, Tat(48-60), and heptaarginine in two different cell lines was studied by confocal laser scanning microscopy. For penetratin, an apparently endocytotic uptake was observed, in disagreement with previous studies on fixed cells found in the literature. Substitution of the two tryptophan residues, earlier reported to be essential for cellular uptake, did not alter the uptake characteristics. A heptaarginine peptide, with a tryptophan residue added in the C-terminus, was found to be internalized by cells via an energy-independent, non-endocytotic pathway. Finally, a crucial role for arginine residues in penetratin and Tat(48-60) was demonstrated.

The antennapedia peptide penetratin translocates across lipid bilayers - the first direct observation.

The potential use of polypeptides and oligonucleotides for therapeutical purposes has been questioned because of their inherently poor cellular uptake. However, the 16‐mer oligopeptide penetratin, derived from the homeodomain of Antennapedia, has been reported to enter cells readily via a non‐endocytotic and receptor‐ and transporter‐independent pathway, even when conjugated to large hydrophilic molecules. We here present the first study where penetratin is shown to traverse a pure lipid bilayer. The results support the idea that the uptake mechanism involves only the interaction of the peptide with the membrane lipids. Furthermore, we conclude that the translocation does not involve pore formation.

Spacelike Singularities and Hidden Symmetries of Gravity

We review the intimate connection between (super-)gravity close to a spacelike singularity (the “BKL-limit”) and the theory of Lorentzian Kac-Moody algebras. We show that in this limit the gravitational theory can be reformulated in terms of billiard motion in a region of hyperbolic space, revealing that the dynamics is completely determined by a (possibly infinite) sequence of reflections, which are elements of a Lorentzian Coxeter group. Such Coxeter groups are the Weyl groups of infinite-dimensional Kac-Moody algebras, suggesting that these algebras yield symmetries of gravitational theories. Our presentation is aimed to be a self-contained and comprehensive treatment of the subject, with all the relevant mathematical background material introduced and explained in detail. We also review attempts at making the infinite-dimensional symmetries manifest, through the construction of a geodesic sigma model based on a Lorentzian Kac-Moody algebra. An explicit example is provided for the case of the hyperbolic algebra E10, which is conjectured to be an underlying symmetry of M-theory. Illustrations of this conjecture are also discussed in the context of cosmological solutions to eleven-dimensional supergravity.

Penetratin-induced aggregation and subsequent dissociation of negatively charged phospholipid vesicles

The interaction of the cellular delivery vector penetratin with a model system consisting of negatively charged phospholipid vesicles has been studied. Above a certain peptide to lipid molar ratio, the cationic oligopeptide induces vesicle aggregation. Interestingly, the aggregation is followed by spontaneous disaggregation, which may be related to membrane translocation of the peptide. Circular dichroism (CD) measurements indicate a conformational transition, from α‐helix to antiparallel β‐pleated sheet, which is simultaneous with the aggregation process. The potential influence of spectroscopic artifacts on CD data due to the drastically increased turbidity during aggregation is discussed.

Wall-crossing, Rogers dilogarithm, and the QK/HK correspondence

A bstractWhen formulated in twistor space, the D-instanton corrected hypermultiplet moduli space in

Packet Video Error Concealment With Gaussian Mixture Models

mathcal{N} = {2}

Fivebrane instantons, topological wave functions and hypermultiplet moduli spaces

string vacua and the Coulomb branch of rigid

Amplifier-Aware Multiple-Input Multiple-Output Power Allocation

mathcal{N} = {2}

Partial Marginalization Soft MIMO Detection With Higher Order Constellations

gauge theories on R3u2009×u2009S1 are strikingly similar and, to a large extent, dictated by consistency with wall-crossing. We elucidate this similarity by showing that these two spaces are related under a general duality between, on one hand, quaternion-Kähler manifolds with a quaternionic isometry and, on the other hand, hyperkähler manifolds with a rotational isometry, equipped with a canonical hyperholomorphic circle bundle and a connection. We show that the transition functions of the hyperholomorphic circle bundle relevant for the hypermultiplet moduli space are given by the Rogers dilogarithm function, and that consistency across walls of marginal stability is ensured by the motivic wall-crossing formula of Kontsevich and Soibelman. We illustrate the construction on some simple examples of wall-crossing related to cluster algebras for rank 2 Dynkin quivers. In an appendix we also provide a detailed discussion on the general relation between wall-crossing and cluster algebras.

Joint Source-Channel Coding for the MIMO Broadcast Channel

In this paper, Gaussian mixture modeling is applied to error concealment for block-based packet video. A Gaussian mixture model for video data is obtained offline and is thereafter utilized online in order to restore lost blocks from spatial and temporal surrounding information. We propose estimators on closed form for missing data in the case of varying available neighboring contexts. Our error concealment strategy increases peak signal-to-noise ratio compared to previously proposed schemes. Examples of improved subjective visual quality by means of the proposed method are also supplied.