Biology subjects

Hoffmann, S.

Publications and source records attributed to Hoffmann, S..

39 records · Page 3Linked to original sources

bioRxiv2019

Structural and functional characterisation of SiiA, an auxiliary protein from the SPI4-encoded type 1 secretion system from Salmonella enterica

Salmonella invasion is mediated by a concerted action of the Salmonella pathogenicity island 4 (SPI4)-encoded type one secretion system (T1SS) and the SPIl-encoded type three secretion system (T3SS-1). The SPI4-encoded T1SS establishes the first contact to the host membrane. It consists of five proteins (SiiABCDF) that secrete the giant adhesin SiiE. The exact mechanism by which the T1SS enables host cell recognition remains unclear. Here, we investigated structure-function relationships in SiiA, a non-canonical T1SS subunit located at the inner membrane (IM). We observe that SiiA consists of a membrane domain, an intrinsically disordered periplasmic linker region and a folded globular periplasmic domain (SiiA-PD). The crystal structure of SiiA-PD shows homology to that of MotB-PD and other peptidoglycan (PG)-binding domains. Indeed, SiiA-PD binds PG in vitro albeit at an acidic pH, only, whereas MotB-PD binds PG from pH 5.8 to 8. Mutation of Arg162 in SiiA impedes PG binding and reduces Salmonella invasion efficacy of polarized epithelial cells. SiiA forms a complex with SiiB at the IM, and the SiiA-MotB homology is likely paralleled by a SiiB-MotA homology. We show that, in addition to PG binding, the SiiAB complex translocates protons across the IM. Substituting Asp13 in SiiA impairs proton translocation. Overall, SiiA displays many properties previously observed in MotB. However, whereas the MotAB complex uses the proton motif force (PMF) to energize the bacterial flagellum, it remains to be shown how the use of the PMF by SiiAB assists T1SS function and ultimately Salmonella invasion.

microbiology↗

bioRxiv2018

Light induced synaptic vesicle autophagy

The regulated turnover of synaptic vesicle (SV) proteins is thought to involve the ubiquitin dependent tagging and degradation through endo-lysosomal and autophagy pathways. Yet, it remains unclear which of these pathways are used, when they become activated and whether SVs are cleared en-mass together with SV proteins or whether both are degraded selectively. Equally puzzling is how quickly these systems can be activated and whether they function in real time to support synaptic health. To address these questions, we have developed an imaging based system that simultaneously tags presynaptic proteins while monitoring autophagy. Moreover, by tagging SV proteins with a light activated reactive oxygen species (ROS) generator, Supernova, it was possible to temporally control the damage to specific SV proteins and assess their consequence to autophagy mediated clearance mechanisms and synaptic function. Our results show that, in mouse hippocampal neurons, presynaptic autophagy can be induced in as little as 5-10 minutes and eliminates primarily the damaged protein rather than the SV en-mass. Importantly, we also find that autophagy is essential for synaptic function, as light-induced damage to e.g. Synaptophysin only compromises synaptic function when autophagy is simultaneously blocked. These data support the concept that presynaptic boutons have a robust highly regulated clearance system to maintain not only synapse integrity, but also synaptic function.

neuroscience↗

bioRxiv2018

Real Time de novo Deposition of Centromeric Histone-associated Proteins Using the Auxin Inducible Degradation System

i.Summary/AbstractMeasuring protein dynamics is essential to uncover protein function and to understand the formation of large protein complexes such as centromeres. Recently, genome engineering in human cells has improved our ability to study the function of endogenous proteins. By combining genome editing techniques with the Auxin Inducible Degradation (AID) system, we created a versatile tool to study protein dynamics. This system allows us to analyze both protein function and dynamics by enabling rapid protein depletion and re-expression in the same experimental set-up. Here, we focus on the dynamics of the centromeric histone-associated protein CENP-C, responsible for the formation of the kinetochore complex. Following rapid removal and re-activation of a fluorescent version of CENP-C by auxin treatment and removal, we could follow CENP-C de novo deposition at centromeric regions during different stages of the cell cycle. In conclusion, the auxin degradation system is a powerful tool to assess and quantify protein dynamics in real time.

cell biology↗