No abstract

Inactivating ADP ribosylation of the ER chaperone BiP is a rapidly reversible mechanism for buffering acute changes in unfolded protein load.

At present, organic molecules are among the best candidate "building blocks" for the construction of self-assembling nanoscale devices based on metal substrates. Control of the formation of specific patterns in the submonolayer regime is usually achieved by appropriate choice and/or functionalization of the adsorbates. The effect of this intervention, though, is limited by the typically short-range character of the bonding. We present here a theoretical study on the system rubrene/gold to show that substrate-induced molecular charging can instead determine the assembly on larger scales. DFT calculations and electrostatic considerations are used to discuss the charge transfer at the metal/organic interface. This allows rationalization of previous puzzling experimental results and, in particular, of the unusual molecular gap broadening upon adsorption observed in STS spectra. The self-assembly process is further studied by means of classical molecular dynamics simulations. The charged adsorbates are modeled as mutually repulsive standing dipoles, with van der Waals interactions intervening at short distances. The striking resemblance between the experimental STM images and the results of our MD simulations shows that this simple model is able to capture the key effects driving the assembly in this system. The competition between long-range repulsive interactions and short-range attractive forces leads to characteristic and easily recognizable 1D patterns. We suggest that experimental evidence of the presence of similar patterns in other metal/organic systems can provide crucial information on the electronic level alignment at the interface, that is, on the occurrence of charge-transfer processes between metal and organic adsorbates.

Glutathione disulfide (GSSG; γ-GluCysGly disulfide) was used as a physiologically relevant model molecule to investigate the fundamental adsorption mechanisms of polypeptides onto α-alumina nanoparticles. Its adsorption/desorption behavior was studied by enzymatic quantification of the bound GSSG combined with zeta potential measurements of the particles. The adsorption of GSSG to alumina nanoparticles was rapid, was prevented by alkaline pH, was reversed by increasing ionic strength, and followed a nearly ideal Langmuir isotherm with a standard Gibbs adsorption energy of -34.7 kJ/mol. Molecular dynamics simulations suggest that only one of the two glutathionyl moieties contained in GSSG binds stably to the nanoparticle surface. This was confirmed experimentally by the release of GSH from the bound GSSG upon reducing its disulfide bond with dithiothreitol. Our data indicate that electrostatic interactions via the carboxylate groups of one of the two glutathionyl moieties of GSSG are predominantly responsible for the binding of GSSG to the alumina surface. The results and conclusions presented here can provide a base for further experimental and modeling studies on the interactions of biomolecules with ceramic materials.

We investigate the dynamical features of the adsorption of diphenylalanine molecules on the Cu(110) surface and of their assembling into supramolecular structures by a combination of quantum and classical atomistic modeling with dynamic scanning tunneling microscopy and spectroscopic experiments. Our results reveal a self-assembling mechanism in which isolated adsorbed molecules change their conformation and adsorption mode as a consequence of their mutual interactions. In particular, the formation of zwitterions after proton transfer between initially neutral molecules is found to be the key event of the assembling process, which stabilizes the supramolecular structures. Because of the constraints on the intermolecular bonds exerted by the surface-molecule interactions, the assembly process is strictly stereoselective, and may suggest a general model for patterning and functionalization of bare metal surfaces with short chiral peptides.

Shrinking devices to the nanoscale, while still maintaining accurate control on their structure and functionality is one of the major technological challenges of our era. The use of purposely directed self‐assembly processes provides a smart alternative to the troublesome manipulation and positioning of nanometer‐sized objects piece by piece. Here, we report on a series of recent works where the in‐depth study of appropriately chosen model systems addresses the two key‐points in self‐assembly: building blocks selection and control of bonding. We focus in particular on hydrogen bonding because of the stability, precision and yet flexibility of nanostructures based on this interaction. Complementing experimental information with advanced atomistic modeling techniques based on quantum formalisms is a key feature of most investigations. We thus highlight the role of theoretical modeling while we follow the progression in the use of more and more complex molecular building blocks, or “tectons”. In particular, we will see that the use of three‐dimensional, flexible tectons promises to be a powerful way to achieve highly sophisticated functional nanostructures. However, the increasing complexity of the assembly units used makes it generally more difficult to control the supramolecular organization and predict the assembling mechanisms. This creates a case for developing novel analysis methods and ever more advanced modeling techniques.

Beleuchtung, Kamera, Aufnahme! Der von Pauling vor mehr als 50 Jahren vorgeschlagene allgemeine Mechanismus der biomolekularen Erkennung wurde nun auf die Leinwand gebracht (siehe Standfoto; D: D‐Phe‐D‐Phe, L: L‐Phe‐L‐Phe). In STM‐Filmen wird der Prozess der chiralen Erkennung einzelner adsorbierter Di(phenylalanin)‐Moleküle verfolgt, um so den dynamischen Induced‐Fit‐Mechanismus auf dem Einzelmolekülniveau zu veranschaulichen.

The authors noted an error in the title of the legend for Fig. 2. A corrected version of the legend is appended below.The html and pdf versions of this article have been corrected. The error remains only in the print version. JCB: CorrectionFigure 2. ADP-ribosylated BiP is enriched in low-molecular weight fractions of the ER extract. (A) Coomassie-stained SDS-PAGE of pancreatic microsomal proteins from fasted and fed mice resolved by gel filtration. BiP is distributed bimodally between a highmolecular weight peak containing the cochaperone ORP150 and GRP94 and lower-molecular weight peak. A representative experiment reproduced three times is shown. Abs., absorbance; mAU, milli-absorbance unit. (B) BiP immunoblot of IEF gels of the input (GF input) and fractions 9 and 14 of the fasted and 1-h refed samples above. The ratio of ADP ribosylated to total BiP in each lane is indicated (R). Black lines indicate that intervening lanes have been spliced out.