BEGIN:VCALENDAR VERSION:2.0 PRODID:icalendar-ruby CALSCALE:GREGORIAN METHOD:PUBLISH BEGIN:VTIMEZONE TZID:Europe/Vienna BEGIN:DAYLIGHT DTSTART:20260329T030000 TZOFFSETFROM:+0100 TZOFFSETTO:+0200 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3 TZNAME:CEST END:DAYLIGHT BEGIN:STANDARD DTSTART:20261025T020000 TZOFFSETFROM:+0200 TZOFFSETTO:+0100 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10 TZNAME:CET END:STANDARD END:VTIMEZONE BEGIN:VEVENT DTSTAMP:20260619T131731Z UID:1782120600@ist.ac.at DTSTART:20260622T113000 DTEND:20260622T123000 DESCRIPTION:Speaker: Jiri Friml & Leonid Sazanov\nhosted by Carl-Philipp He isenberg\nAbstract: Auxin Signalling: Deconstructing a Long-Standing Parad igm in Plant BiologyAuxin is a major endogenous regulator of plant growth and development and one of the longest-studied plant hormones. The discove ry that auxin induces the transcription of hundreds of genes enabled the i dentification of key transcriptional regulators: Auxin Response Factors (A RFs) and their repressors\, the Aux/IAA (Auxin/Indole-3-acetic acid) prote ins. In parallel\, genetic screens for auxin-insensitive mutants uncovered components of the ubiquitin ligase machinery responsible for targeted pro tein degradation\, most notably TIR1 (Transport Inhibitor Response 1)\, an F-box component of the ubiquitin ligase complex.The resulting model is re markably simple: auxin promotes the interaction between TIR1-type auxin re ceptors and Aux/IAA co-receptors. This leads to Aux/IAA ubiquitination and degradation\, releasing ARFs from repression and enabling transcriptional responses. The model elegantly explained existing observations\, inspired the discovery of analogous repressor-degradation mechanisms in other path ways\, and withstood the test of time for more than two decades.Neverthele ss\, live imaging using a vertical-stage microscope developed at ISTA reve aled that auxin-induced root growth inhibition occurs within 30 seconds— far too rapidly to involve transcription. This finding led to the discover y that TIR1-type receptors also function as adenylyl cyclases (ACs)\, enzy mes that produce cyclic AMP (cAMP)\, a prominent second messenger in anima l cells. Subsequent studies demonstrated that cAMP is an indispensable com ponent of auxin signal transduction\, fundamentally challenging the canoni cal model of auxin action.Here\, I will trace the history of auxin signall ing\, from its discovery to the unexpected revisions that have recently re shaped the field.____________A Huge Molecular Proton Pump - How Complex I Works?Mitochondria are the “powerhouses” of eukaryotes. Mitochondrial (and often bacterial) respiratory chains comprise several large\, inner-me mbrane-embedded protein assemblies. Complexes I\, III\, and IV create a pr oton gradient across the membrane\, which then drives the rotary ATP synth ase. This system powers life by continuously providing ATP—humans turn o ver roughly their body weight of this energy-rich molecule every day. We s tudy the structure and mechanism of these enzymes and their supercomplexes using cryogenic electron microscopy (cryo-EM) and functional assays.Compl ex I is the first and largest enzyme in the chain\, consisting of up to 45 different subunits with a total molecular mass of about 1 MDa. It couples the transfer of two electrons from NADH to ubiquinone to the translocatio n of four protons across the membrane by a mechanism that is still hotly d ebated. Complex I has three antiporter-like subunits plus one additional s imilar domain\, which were previously thought to be responsible for pumpin g one proton each per catalytic cycle.We have solved high-resolution cryo- EM structures of complex I from several mammalian\, yeast\, and bacterial species under various conditions\, including catalytic turnover. Unexpecte dly\, we demonstrated that only one distal antiporter-like subunit is capa ble of ejecting protons into mitochondrial intermembrane space (or bacteri al periplasm). Dramatic conformational changes around the quinone-binding cavity couple the redox reaction to proton translocation during “open-to -closed” state transitions of the enzyme. In the “open” state\, the Q-cavity is widely open\, allowing quinone to enter and exit. In the “cl osed” state\, the cavity is tightly enclosed around the bound quinone\, meaning the protons needed to complete quinone reduction must originate fr om the central axis of the membrane domain. This initiates a “domino-eff ect” cascade of electrostatic interactions within the antiporter-like su bunits\, ultimately resulting in the ejection of four protons per catalyti c cycle from the distal subunit.Our proposed mechanism for complex I is an unexpected combination of conformational changes and electrostatic intera ctions. It challenges the paradigm held over the last decade\, yet it is r obust and explains all the unique features of complex I resolved in recent structural studies. LOCATION:Raifeisen Lecture Hall\, ISTA ORGANIZER:diana.zubcevic@ista.ac.at SUMMARY:Jiri Friml & Leonid Sazanov: Auxin Signalling: Deconstructing a Lon g-Standing Paradigm in Plant Biology & A Huge Molecular Proton Pump - How Complex I Works? URL:https://talks-calendar.ista.ac.at/events/6481 END:VEVENT END:VCALENDAR