Plants and photosynthetic bacteria contain protein−molecular complexes that harvest photons with nearly optimum quantum yield and an expected power conversion efficiency exceeding 20%. In this work, we demonstrate the integration of electrically active photosynthetic protein− molecular complexes in solid-state devices, realizing photodetectors and photovoltaic cells with internal quantum efficiencies of approximately 12%. Electronic integration of devices is achieved by self-assembling an oriented monolayer of photosynthetic complexes, stabilizing them with surfactant peptides, and then coating them with a protective organic semiconductor.

The fidelity and specificity of information flow within a cell is controlled by scaffolding proteins that assemble and link enzymes into signalling circuits1,2. These circuits can be inhibited by bacterial effector proteins that post-translationally modify individual pathway components3–6. However, there is emerging evidence that pathogens directly organize higher-order signalling networks through enzyme scaffolding7,8, and the identity of the effectors and their mechanisms of action are poorly understood. Here we identify the enterohaemorrhagic Escherichia coli O157:H7 type III effector EspG as a regulator of endomembrane trafficking using a functional screen, and report ADP-ribosylation factor (ARF) GTPases and p21-activated kinases (PAKs) as its relevant host substrates. The 2.5 Å crystal structure of EspG in complex with ARF6 shows how EspG blocks GTPase-activating-protein-assisted GTP hydrolysis, revealing a potent mechanism of GTPase signalling inhibition at organelle membranes. In addition, the 2.8 Å crystal structure of EspG in complex with the autoinhibitory Iα3-helix of PAK2 defines a previously unknown catalytic site in EspG and provides an allosteric mechanism of kinase activation by a bacterial effector. Unexpectedly, ARF and PAKs are organized on adjacent surfaces of EspG, indicating its role as a ‘catalytic scaffold’ that effectively reprograms cellular events through the functional assembly of GTPase-kinase signalling complex.

The innate immune system has evolved under selective pressure since the radiation of multicellular life approximately six hundred million years ago. Because of this long history, innate immune mechanisms found in modern eukaryotic organisms today are highly complex, yet are built from common molecular strategies. It is now clear that evolution has selected a conserved set of anti-microbial peptides as well as Pattern Recognition Receptors (PRRs) that initiate cellular-based signals as a first line of defense against invading pathogens. Conversely, microbial pathogens employ their own strategies to evade, inhibit, or otherwise manipulate the innate immune response. Here, we discuss recent discoveries that have changed our view of immune modulatory mechanisms employed by bacterial pathogens, focusing specifically on the initial sites of microbial recognition and extending to host cellular signal transduction, pro-inflammatory cytokine production, and alteration of protein trafficking and secretion.

Despite the availability of thousands of transit peptide (TP) primary sequences, the structural and/or physicochemical properties that determine TP recognition by components of the chloroplast translocon are not well understood. By combining a series of in vitro and in vivo experiments, we reveal that TP recognition is determined by sequence-independent interactions and vectorial-specific recognition domains. Using both native and reversed TPs for two well-studied precursors, small subunit of ribulose-1,5-bis-phosphate carboxylase/oxygenase, and ferredoxin, we exposed these two modes of recognition. Toc34 receptor (34-kD subunit of the translocon of the outer envelope) recognition in vitro, preprotein binding in organellar, precursor binding in vivo, and the recognition of TPs by the major stromal molecular motor Hsp70 are specific for the physicochemical properties of the TP. However, translocation in organellar and in vivo demonstrates strong specificity to recognition domain organization. This organization specificity correlates with the N-terminal placement of a strong Hsp70 recognition element. These results are discussed in light of how individual translocon components sequentially interact with the precursor during binding and translocation and helps explain the apparent lack of sequence conservation in chloroplast TPs.