2016-2018


  • Project Area A: Substrate Identification and Validation
  • Project Area B: Substrate Recognition, Cleavage & TM Helix Dynamics
  • Project Area C: Comparing Substrates by Sequence and Conformational Dynamics: Biophysics & Bioinformatics

Project Area A


Substrate identification and validation


 

 A major aim of our research group is to understand what molecular features qualify a membrane protein as a substrate for intramembrane proteolysis. Answering this question is not only essential to elucidate the physiological function of a protease and evaluate its potential as a drug target but also to understand how a protease recognizes its substrates and cleaves them mechanistically and to elucidate how a protease differs from related proteases. In order to address this question it is necessary to identify the membrane proteins that are cleaved by a protease (substrates) and those membrane proteins that are not cleaved (non-substrates).

 

Combining methods from biochemistry (such as domain swap experiments, together with P4 and P6), bioinformatics (sequence comparisons, together with P7) and biophysics (analyzing structural parameters, together with P5 and P8) will then allow elucidating the molecular characteristics that qualify a membrane protein as a protease substrate. Among the four major families of intramembrane proteases – rhomboids, SPP/SPPLs, g-secretase and S2Ps – we focus on three for substrate identification and mechanistic analysis, namely PARL, the SPPL2 subfamily and γ-secretase.

 


 

Project P1: Marius Lemberg

 

Defining the physiological substrate spectrum and the cleavage site specificity of the mitochondrial rhomboid protease PARL

 

ZMBH Heidelberg


 

Project P2: Regina Fluhrer

 

Substrate Portfolio of the Signal Peptide Peptidase-like 2 (SPPL2) family

 

LMU and DZNE Munich


 

Project P3: Stefan Lichtenthaler

 

Identification and mechanistic characterization of a new class of γ-secretase substrates and non-substrates with short extracellular domains

 

TUM and DZNE Munich


Project Area B


Substrate recognition, cleavage & TM helix dynamics 


Recent data suggest that intramembrane proteolysis is a surprisingly slow process whose overall kinetics is composed of the kinetics of several steps. These steps may include:

  • substrate recognition by an exosite on the protease,
  • subsequent conformational changes of the substrate/enzyme complex to expose the scissile amide bonds to the catalytic residues,
  • formation of the tetrahedral intermediate leading to hydrolysis, and
  • product release

It is currently unclear which of the above step(s) limit the rate of proteolysis, how the ratelimiting step(s) depend on the primary structures and/or the conformational dynamics of the substrates, how disease-related point mutations affect these properties and which step(s) are relevant for substrate/non-substrate discrimination. Furthermore, we do not know whether all intramembrane proteases employ exosites for substrate binding, where they are located, and whether substrates are recognized and/or cleaved as monomers or multimers.

 


 

Project P4: Harald Steiner

 

Substrate recognition and cleavage by γ-secretase

 

LMU and DZNE Munich


 

Project P5: Dieter Langosch

 

The Conformational Flexibility of Transmembrane Helices in Substrate Recognition and Cleavage

 

TUM Munich


 

Project P6: Christian Haass

 

Role of transmembrane domain interactions for γ-secretase substrate recognition using the TREM2/DAP12 complex

 

LMU and DZNE Munich


Project Area C


 Comparing substrates by sequence and conformational dynamics: biophysics & bioinformatics


Although no structure of a substrate/enzyme complex is currently available, it is informative to study the intrinsic dynamics of isolated substrates. This is justified by the observation that an isolated protein already exhibits the types of structural changes that may occur after binding to other proteins. Helices are indeed quite adaptable as almost half of the TM domains within crystallized membrane proteins contain non-canonical Elements and exhibit different curvatures.

 A combined experimental and computational effort will be directed at unravelling the fine details of TM helix flexibility for two paradigmatic substrates, C99 and PINK1.

Several backbone NMR structures have been published for C99  while PINK1 is completely uncharted territory.

In sum, this will show the commonalities and the differences in structural dynamics of substrate TM helices that are proteolyzed by different enzymes i) by providing descriptors of the global TM domain dynamics, i.e., bending, twisting and stretching modes location of hinges, and ii) by characterizing local features like side-chain packing, hydrogen-bond occupancies, local hydration and cooperative local unfolding at cleavage sites. Importantly, these analysis will also reveal the structural and dynamical impact of mutations that alter proteolytic processing by linking them to experiments in Aim 2. This will allow us to extract those conformational and dynamical features that are relevant at different steps of substrate proteolysis!


Project P7: Christina Scharnagl, Dmitrij Frishman

 

Sequence requirements, conformational flexibility, and functional networks of intramembrane protease substrates



Project P8: Burkhard Luy, Daniel Huster

 

Investigation of Molecular Dynamics of Substrate Transmembrane α-Helices by Solution and Solid-State NMR Spectroscopy

 



 

Project P9: Stefan Lichtenthaler

 

Proteomic Platform

 

TUM and DZNE Munich


Research Unit FOR 2290