Biology subjects

Brennich, M.

Publications and source records attributed to Brennich, M..

3 recordsLinked to original sources

bioRxiv2020

Structural basis of client specificity in mitochondrial membrane-protein chaperones

Chaperones are essential for assisting protein folding, and for transferring poorly soluble proteins to their functional locations within cells. Hydrophobic interactions drive promiscuous chaperone-client binding, but our understanding how additional interactions enable client specificity is sparse. Here we decipher what determines binding of two chaperones (TIM8{middle dot}13, TIM9{middle dot}10) to different integral membrane proteins, the alltransmembrane mitochondrial carrier Ggc1, and Tim23 which has an additional disordered hydrophilic domain. Combining NMR, SAXS and molecular dynamics simulations, we determine the structures of Tim23/TIM8{middle dot}13 and Tim23/TIM9{middle dot}10 complexes. TIM8{middle dot}13 uses transient salt bridges to interact with the hydrophilic part of its client, but its interactions to the trans-membrane part are weaker than in TIM9{middle dot}10. Consequently, TIM9{middle dot}10 is outcompeting TIM8{middle dot}13 in binding hydrophobic clients, while TIM8{middle dot}13 is tuned to few clients with both hydrophilic and hydrophobic parts. Our study exemplifies how chaperones fine-tune the balance of promiscuity vs. specificity.

biophysics↗

bioRxiv2020

Architecture and subunit dynamics of the mitochondrial TIM9·10·12 chaperone

The mitochondrial Tim chaperones are responsible for the transport of membrane proteins across the inter-membrane space to the inner and outer mitochondrial membranes. TIM9{middle dot}10, a hexameric 70 kDa protein complex formed by 3 copies of Tim9 and Tim10, guides its clients across the aqueous compartment. The TIM9{middle dot}10{middle dot}12 complex is the anchor point at the inner-membrane insertase complex TIM22. The subunit composition of the TIM9{middle dot}10{middle dot}12 complex remains debated. Joint NMR, small-angle X-ray scattering and MD simulation data allow us to derive a structural model of the TIM9{middle dot}10{middle dot}12 assembly, which has a 2:3:1 stoichiometry (Tim9:Tim10:Tim12). We find that both TIM9{middle dot}10 and TIM9{middle dot}10{middle dot}12 hexamers are in a dynamic equilibrium with their constituent subunits, exchanging on a minutes time scale. Residue-resolved NMR data establish that the subunits exhibit large conformational dynamics: when the conserved cysteines of the CX3C-Xn-CX3C motifs are formed, short marginally stable -helices are formed, and these are fully stabilized only upon formation of the mature hexameric chaperone. We propose that the continuous subunit exchange is a means of mitochondria to control their level of inter-membrane space chaperones, and thus rapidly adapt to the cellular state.

biophysics↗

bioRxiv2018

Deciphering copper coordination in the animal prion protein amyloidogenic domain

Prions are pathological isoforms of the cellular prion protein (PrPC) responsible for transmissible spongiform encephalopathies (TSE). PrPC interacts with copper through unique octarepeat and non-octarepeat (non-OR) binding sites. Previous works on human PrPC suggest that copper binding to the non-OR region may have a role during prion conversion. The molecular details of copper coordination within the non-OR region are not well characterized. By means of small angle X-ray scattering (SAXS) and extended X-ray absorption fine structure (EXAFS) spectroscopy, we have investigated the Cu(II) structural effects on the protein folding and its coordination geometries when bound to the non-OR region of recombinant PrPC (recPrP) from animal species considered high or less resistant to TSE. As TSE-resistant model, we used ovine PrPC carrying the protective polymorphism at residues A136, R154 and R171 (OvPrP ARR); while as highly TSE-susceptible PrPC models we employed OvPrP with polymorphism V136, R154 and Q171 (OvPrP VRQ) and Bank vole recPrP (BvPrP). Our results reveal that Cu(II) affects the structural plasticity of the non-OR region leading to a more compacted conformation of recPrP. We also identified two Cu(II) coordinations in the non-OR region of these animal species. In type-1 coordination present in OvPrP ARR, Cu(II) is coordinated by four residues (S95, Q98, M109 and H111). Conversely, the type-2 coordination is present in OvPrP VRQ and BvPrP, where Cu(II) is coordinated by three residues (Q98, M109 and H111) and by one water molecule, making the non-OR region more flexible and open to the solvent. These changes in copper coordination in prion resistant and susceptible species provide new insights into the molecular mechanisms governing the resistance or susceptibility of certain species to TSE.

biochemistry↗