It works both ways: The mechanism of electron transfer through peptides depends upon the side chain X located between the electron donor and the electron acceptor. Electron transfer occurs either by a slow single‐step superexchange or by a two‐step hopping process that is 20–30‐times faster (see scheme). All intermediates in the hopping process could be observed simultaneously.

Cell activation initiated by receptor ligands or oncogenes triggers complex and convoluted intracellular signaling. Techniques initiating signals at defined starting points and cellular locations are attractive to elucidate the output of selected pathways. Here, we present the development and validation of a protein heterodimerization system based on small molecules cross-linking fusion proteins derived from HaloTags and SNAP-tags. Chemical dimerizers of HaloTag and SNAP-tag (HaXS) show excellent selectivity and have been optimized for intracellular reactivity. HaXS force protein-protein interactions and can translocate proteins to various cellular compartments. Due to the covalent nature of the HaloTag-HaXS-SNAP-tag complex, intracellular dimerization can be easily monitored. First applications include protein targeting to cytoskeleton, to the plasma membrane, to lysosomes, the initiation of the PI3K/mTOR pathway, and multiplexed protein complex formation in combination with the rapamycin dimerization system.

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Abstract:We have designed and synthesized a peptide model in which stepwise electron transfer (ET) through amino acid side chains could be observed. An injection system, which generates an electron hole upon laser irradiation, was connected directly to the aromatic side chain of a modified C-terminal amino acid. This electron acceptor could be observed by transient absorption spectroscopy. The N-terminal amino acid tyrosine acts as an electron donor, giving a different signal in the transient absorption spectrum. Additional non-natural oxidizable aromatic amino acids were synthesized as spectroscopic sensors to detect oxidized amino acid side chains as chemical intermediates in long range ET.

Springende Löcher: Oligopeptide mit einem photosensiblen Ladungsinjektionssystem wurden hergestellt und mit einem Nanosekundenlaser bestrahlt. Dabei trat ein mehrstufiger Elektronentransport auf, der aromatische Seitenketten als Lochträger nutzt (siehe Schema). Die Geschwindigkeit dieses Prozesses spricht für einen Elektronentransfer durch den Raum (einen Hopping‐Mechanismus).