A long-standing project in the group is dedicated to investigation of structure-function relationships of two multicomponent chaperone systems involved in assembly of bacterial and human respiratory complexes, and thereby in antibiotic resistance and in Alzheimer disease respectively. Even though we have made great strides in understanding both systems, many questions still linger.
Unravelling the structure and the roles of the mitochondrial Complex I assembly complex in Alzheimer’s disease
Catarina S. Silva, Ambroise Desfosses, Maria Bacia, Irina Gutsche
Worldwide research efforts to identify the factors driving Alzheimer’s disease (AD) pathogenesis aim to find better ways to diagnose, delay and prevent the disease progression. For energy uptake, neurons rely on an efficient oxidative metabolism and are therefore particularly sensitive to mitochondrial dysfunctions. Respiratory Complex I (CI), the first enzyme in the respiratory chain, is crucial for energy production driven by oxidative phosphorylation and is thought to be linked to AD pathophysiology. We use cryo-EM to investigate the human Mitochondrial Complex I Assembly (MCIA) complex, essential for the CI biogenesis. Indeed, the organisation of MCIA and the mechanism of its action on CI remain unclear, in part because the core components of the MCIA complex - ACAD9, ECSIT and NDUFAF1 – also perform multiple other cellular functions. ECSIT, for example, is involved in cytoplasmic and nuclear signalling pathways, undergoes post-translational modifications and has been reported to interact with amyloid-β (Aβ) producing enzymes. Together with our collaborators in ESRF, and making use of an integrative structural biology approach, we aim to elucidate in molecular detail the function of the MCIA complex in CI assembly, its roles in mitochondrial bioenergetics and its interplay with amyloidogenic Aβ, a hallmark of AD.
Collaborations :
– Montserrat Soler-Lopez, ESRF, Grenoble
Investigation of the molecular mechanisms of action of the enterobacterial LdcI-RavA-ViaA triad in stress response and antibiotic resistance
Moritz Kirchner, Madalen Le Gorrec, Maria Bacia, Irina Gutsche
To spread through our digestive system, enterobacteria must survive antibiotic exposure in the acidic and anaerobic conditions of the host stomach. Toxicity of the highly efficient aminoglycoside (AG) antibiotics, limits their use to severe infections only. Moreover, their activity decreases under anaerobiosis, requiring even higher therapeutic doses. Reducing AG doses should minimise toxicity and expand their safer use. To achieve this, it is essential to understand what makes enterobacteria sensitive to AGs in gastrointestinal tract conditions. Since many years, our group has been studying a tricomponent enterobacterial stress response system composed of an acid inducible lysine decarboxylase LdcI, its AAA+ ATPase regulator RavA and a RavA partner ViaA. This system was proposed to chaperone respiratory complexes, in particular CI and fumarate reductase, thereby facilitating AG uptake. However, although our collaborators confirmed that the ravAviaA operon was essential for bactericidal activity of AGs under anaerobiosis, its mechanism of action remained controversial. Recently, we discovered that RavA and ViaA are at the heart of a previously unknown pathway, mobilised in response to AGs under anaerobiosis and engaged in cell membrane regulation via direct binding to specific lipids. We demonstrated that RavA and ViaA locally modify membrane composition and morphology, thereby facilitating the entry of antibiotics into the bacteria in a respiratory complexes-dependent manner. This breakthrough has set the stage for further investigations of the molecular network that links the LdcI-RavA-ViaA triad to stress response, membrane homeostasis and remodelling, respiration and AG sensitivity. In this context, we use a combination of advanced optical imaging, single particle cryo-EM and cryo-ET to decipher the modes of action of the LdcI-RavA-ViaA triad in membrane biology and stress adaptation.
Collaborations :
– Jean-Philippe Kleman, M4D platform, I2SR, IBS
– Frédéric Barras, Pasteur Institute, Paris
– Daniel Castaño Díez, CSIC, Bilbao, Spain
– Mikhail Bogdanov, University of Texas, USA