Tilmann Häupl

Biocompatible Silicon Surfaces through Orthogonal Click Chemistries and a High Affinity Silicon Oxide Binding Peptide

Multifunctionality is gaining more and more importance in the field of improved biomaterials. Especially peptides feature a broad chemical variability and are versatile mediators between inorganic surfaces and living cells. Here, we synthesized a unique peptide that binds to SiO(2) with nM affinity. We equipped the peptide with the bioactive integrin binding c[RGDfK]-ligand and a fluorescent probe by stepwise Diels-Alder reaction with inverse electron demand and copper(I) catalyzed azide-alkyne cycloaddition. For the first time, we report the generation of a multifunctional peptide by combining these innovative coupling reactions. The resulting peptide displayed an outstanding binding to silicon oxide and induced a significant increase in cell spreading and cell viability of osteoblasts on the oxidized silicon surface.

The influence of the ΔK280 mutation and N- or C-terminal extensions on the structure, dynamics, and fibril morphology of the tau R2 repeat

Tau is a microtubule-associated protein and is involved in microtubule assembly and stabilization. It consists of four repeats that bind to the microtubule. The ΔK280 deletion mutation in the tau R2 repeat region is directly associated with the development of the frontotemporal dementia parkinsonism linked to chromosome 17 (FTDP-17). This deletion mutation is known to accelerate tau R2 repeat aggregation. However, the secondary and the tertiary structures of the self-assembled ΔK280 tau R2 repeat mutant aggregates are still controversial. Moreover, it is unclear whether extensions by one residue in the N- or the C-terminus of this mutant can influence the secondary or the tertiary structure. Herein, we combine solid-state NMR, atomic force microscopy, electron microscopy and all-atom explicit molecular dynamics simulations to investigate the effects of the deletion mutation and the N- and the C-terminal extension of this mutant on the structure. Our main findings show that the deletion mutation induces the formation of small aggregates, such as oligomers, and reduces the formation of fibrils. However, the extensions in the N- or the C-terminus revealed more fibril formation than small aggregates. Further, in the deletion mutation only one structure is preferred, while the N- and the C-terminal extensions strongly lead to polymorphic states. Finally, our broad and combined experimental and computational techniques provide direct structural information regarding ΔK280 tau R2 repeat mutant aggregates and their extensions in the N- and C-terminii by one residue.

Chemical Modification of a Tetrapyrrole-Type Photosensitizer: Tuning Application and Photochemical Action beyond the Singlet Oxygen Channel

Reactive oxygen species (ROS) formed by light activated photosensitizers (PSs) are the hallmark of photodynamic therapy (PDT). It is generally accepted that commonly used PSs generate singlet oxygen ((1)O2) as the cell-toxic species via type II photosensitization. We explored here the consequences of chemical modification and the influence of the net charge of a cationic tetrahydroporphyrin derivative (THPTS) relative to the basic molecular structure on the red-shift of absorption, solubility, mechanistic features, and photochemical as well as cell-toxic activity. In order to shed light into the interplay between chemical modification driven intra- and intermolecular photochemistry, intermolecular interaction, and function, a number of different spectroscopic techniques were employed and our experimental studies were accompanied by quantum chemical calculations. Here we show that for THPTS neither (1)O2 nor other toxic ROS (superoxide and hydroxyl radicals) are produced directly in significant quantities in aqueous solution (although the formation of singlet oxygen is energetically feasible and as such observed in acetonitrile). Nevertheless, the chemically modified tetrapyrrole photosensitizer displays efficient cell toxicity after photoexcitation. The distribution and action of THPTS in rat bladder caricinoma AY27 cells measured with fluorescence lifetime imaging microscopy shows accumulation of the THPTS in lysosomes and efficient cell death after irradiation. We found evidence that THPTS in water works mainly via the type I mechanism involving the reduction rather than oxidation of the excited triplet state THPTS(T1) via efficient electron donors in the biosystem environment and subsequent electron transfer to produce ROS indirectly. These intriguing structure-activity relationships may indeed open new strategies and avenues in developing PSs and PDT in general.

A Detailed Analysis of the Morphology of Fibrils of Selectively Mutated Amyloid β (1–40)

A small library of rationally designed amyloid β [Aβ(1-40)] peptide variants is generated, and the morphology of their fibrils is studied. In these molecules, the structurally important hydrophobic contact between phenylalanine 19 (F19) and leucine 34 (L34) is systematically mutated to introduce defined physical forces to act as specific internal constraints on amyloid formation. This Aβ(1-40) peptide library is used to study the fibril morphology of these variants by employing a comprehensive set of biophysical techniques including solution and solid-state NMR spectroscopy, AFM, fluorescence correlation spectroscopy, and XRD. Overall, the findings demonstrate that the introduction of significant local physical perturbations of a crucial early folding contact of Aβ(1-40) only results in minor alterations of the fibrillar morphology. The thermodynamically stable structure of mature Aβ fibrils proves to be relatively robust against the introduction of significantly altered molecular interaction patterns due to point mutations. This underlines that amyloid fibril formation is a highly generic process in protein misfolding that results in the formation of the thermodynamically most stable cross-β structure.