Biology subjects

Stierhof, Y.-D.

Publications and source records attributed to Stierhof, Y.-D..

3 recordsLinked to original sources

bioRxiv2022

Cell specialization in cyanobacterial biofilm development revealed by expression of a cell-surface and extracellular matrix protein

Cyanobacterial biofilms are ubiquitous and play important roles in diverse environments, yet, understanding of the processes underlying development of these aggregates is just emerging. Here we report cell specialization in formation of Synechococcus elongatus PCC 7942 biofilms - a hitherto unknown characteristic of cyanobacterial multicellularity. We show that only a quarter of the cell population expresses at high levels the four-gene ebfG-operon that is required for biofilm formation. Almost all cells, however, are assembled in the biofilm. Detailed characterization of EbfG4 encoded by this operon revealed cell-surface localization as well as its presence in the biofilm matrix. Moreover, EbfG1-3 were shown to form amyloid structures such as fibrils and are thus likely to contribute to the matrix structure. These data suggest a beneficial division of labour during biofilm formation where only some of the cells allocate resources to produce matrix proteins - public goods that support robust biofilm development by the majority of the cells. Additionally, previous studies revealed the operation of a self-suppression mechanism that depends on an extracellular inhibitor, which supresses transcription of the ebfG-operon. Here we revealed inhibitor activity at an early growth stage and its gradual accumulation along the exponential growth phase in correlation with cell density. Data, however, do not support a threshold-like phenomenon known for quorum-sensing in heterotrophs. Together, data presented here demonstrate cell specialization and imply density-dependent regulation thereby providing novel insights into cyanobacterial communal behaviour. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=98 SRC="FIGDIR/small/498973v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@7758f8org.highwire.dtl.DTLVardef@172396aorg.highwire.dtl.DTLVardef@176612org.highwire.dtl.DTLVardef@2e320c_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2020

Polycationic gold nanorods as multipurpose in vitro microtubule markers

Gold nanoparticles are intriguing because of their unique size- and shape-dependent chemical, electronic and optical properties. Various microscopy and biomedical applications are based on the particles biocompatibility, surface functionalizability, light absorption, and plasmon resonances. Gold nanorods (AuNRs) are particularly promising for various sensor applications due to their tip-enhanced plasmonic fields. For biomolecule attachment, AuNRs are often stabilized with amphiphilic molecules and functionalized with antibodies or biotin-binding proteins. However, by their intrinsic size such molecules block the most sensitive near-field region of the AuNRs. Here, we used short cationic thiols to covalently functionalize the gold surface. We show that the functionalization layer is thin and that these polycationic AuNRs bind in vitro to negatively charged microtubule filaments. Furthermore, we can plasmonically stimulate light emission from the AuNRs and, therefore, use them as bleach- and blinkfree microtubule markers. We confirmed colocalization by transmission electron microscopy or the combination of interference reflection and single-molecule fluorescence microscopy of fluorescently-labeled or plasmonic photoluminescent versions of the AuNRs. We expect that polycationic AuNRs may be applicable to in vivo systems and other negatively charged molecules like DNA. In the long-term, microtubule-bound AuNRs can be used as ultrasensitive single-molecule sensors for molecular machines that interact with microtubules.

biophysics↗

bioRxiv2020

ARF1 dimerization is essential for vesicle trafficking and dependent on activation by ARF-GEF dimers in Arabidopsis

Membrane traffic maintains the organization of the eukaryotic cell and delivers cargo proteins to their subcellular destinations such as sites of action or degradation. Membrane vesicle formation requires ARF GTPase activation by the SEC7 domain of ARF guanine-nucleotide exchange factors (ARF-GEFs), resulting in the recruitment of coat proteins by GTP-bound ARFs. In vitro exchange assays were done with monomeric proteins, although ARF-GEFs have been shown to form dimers in vivo. This feature is conserved across the eukaryotes, however its biological significance is unknown. Here we demonstrate ARF1 dimerization in vivo and we show that ARF-GEF dimers mediate ARF1 dimer formation. Mutational disruption of ARF1 dimers interfered with ARF1-dependent trafficking but not coat protein recruitment in Arabidopsis. Mutations disrupting simultaneous binding of two ARF1*GDPs by the two SEC7 domains of GNOM ARF-GEF dimer prevented stable interaction of ARF1 with ARF-GEF and thus, efficient ARF1 activation. Our results suggest a model of activation-dependent dimerization of membrane-inserted ARF1*GTP molecules required for coated membrane vesicle formation. Considering the evolutionary conservation of ARFs and ARF-GEFs, this initial regulatory step of membrane trafficking might well occur in eukaryotes in general.

plant biology↗