One- and two-color photon echo peak shift studies of photosystem I

Wavelength-dependent one- and two-color photon echo peak shift spectroscopy was performed on the chlorophyll Qy band of trimeric photosystem I from Thermosynechococcus elongatus. Sub-100 fs energy transfer steps were observed in addition to longer time scales previously measured by others. In the main PSI absorption peak (675-700 nm), the peak shift decays more slowly with increasing wavelength, implying that energy transfer between pigments of similar excitation energy is slower for pigments with lower site energies. In the far-red region (715 nm), the decay of the peak shift is more rapid and is complete by 1 ps, a consequence of the strong electron-phonon coupling present in this spectral region. Two-color photon echo peak shift data show strong excitonic coupling between pigments absorbing at 675 nm and those absorbing at 700 nm. The one- and two-color peak shifts were simulated using the previously developed energy transfer model (J. Phys. Chem. B 2002, 106, 10251; Biophysical Journal 2003, 85, 140). The simulations agree well with the experimental data. Two-color photon echo peak shift is shown to be far more sensitive to variations in the molecular Hamiltonian than one-color photon echo peak shift spectroscopy.     

Adsorption of fumaramide [2]rotaxane and its components on a solid substrate: a coverage-dependent study

The coverage-dependent adsorption on Au(111) of a fumaramide [2]rotaxane and its components, a benzylic amide macrocycle and a fumaramide thread, is studied using high-resolution electron energy loss spectroscopy (HREELS). Up to monolayer coverage, the relative intensity of out-of-plane to in-plane phenyl ring vibrational modes indicates that the macrocycle adopts an orientation with the phenyl rings largely parallel to the surface. The formation of a chemisorption bond is evidenced by the presence of a Au-O stretching vibration. In contrast, the thread shows no evidence of chemisorption or a preferential orientation. The introduction of the thread into the macrocycle partly disrupts the film order so that the resulting chemisorbed rotaxane shows intermediate behavior with a preferential orientation up to 0.5 ML coverage. A decrease in film order and the absence of a preferred molecular orientation is observed for all three molecules at multilayer coverages. The spectral differences are addressed by molecular dynamics simulations in terms of the mobility of the phenyls of the three molecules on Au(111).     

Tumor-Cell-Specific Targeting of Ibrutinib: Introducing Electrostatic Antibody-Inhibitor Conjugates (AiCs)

Ibrutinib is an inhibitor of Bruton's tyrosine kinase that has been approved for the treatment of patients with chronic lymphocytic leukemia, mantle cell lymphoma and Waldenstrom's macroglobulinemia and is connected with toxicities. To minimize its toxicities, we linked ibrutinib to a cell-targeted, internalizing antibody. To this end, we synthesized a poly-anionic derivate, ibrutinib-Cy3.5, that retains full functionality. This anionic inhibitor is complexed by our anti-CD20-protamine targeting conjugate and free protamine, and thereby spontaneously assembles into an electrostatically stabilized vesicular nanocarrier. The complexation led to an accumulation of the drug driven by the CD20 antigen internalization to the intended cells and an amplification of its pharmacological effectivity. In vivo, we observed a significant enrichment of the drug in xenograft lymphoma tumors in immune-compromised mice and a significantly better response to lower doses compared to the original drug.     

Evolved,Selective Erasers of Distinct Lysine Acylations

Lysine acylations, a family of diverse protein modifications varying in acyl‐group length, charge, and saturation, are linked to many important physiological processes. Only a small set of substrate‐promiscuous lysine acetyltransferases and deacetylases (KDACs) install and remove this vast variety of modifications. Engineered KDACs that remove only one type of acylation would help to dissect the different contributions of distinct acylations. We developed a bacterial selection system for the directed evolution of KDACs and identified variants up to 400 times more selective for butyryl‐lysine compared to crotonyl‐lysine. Structural analyses revealed that the enzyme adopts different conformational states depending on the type of acylation of the bound peptide. We used the butyryl‐selective KDAC variant to shift the cellular acylation spectrum towards increased lysine crotonylation. These new enzymes will help in dissecting the roles of different lysine acylations in cell physiology.