Biochemistry of Signal Dynamics

Communication is crucial in biology. This is also true for the cells in our body, which make sure that signals occur at the right place and right time. This is achieved by controlling when and where signalling molecules become actived, and subsequently deactivated once the signal needs to be switched off. The regulation of these biochemical switches in signal-transducing systems is typically achieved by chemically modifying signalling proteins or complexes through reversible post-translational modifications (PTMs; Figure 1a). 

Figure 1: HORMA domains provide an alternative mechanism to create a dynamic spatio-temporal controlled signal transduction.

HORMA domains are unique signalling modules
The primary interest of our research group is in a less studied alternative process in cellular signalling, which is operational in cell division, DNA damage signalling, and autophagy. Central to this process is the extraordinary ability of HORMA protein domains to wrap their C-terminal tail around an interacting peptide motif, thereby creating a very stable but temporary signalling complex (Figure 1b). In order to understand how this results in a signalling process, we have previously biochemically reconstituted a near-complete signal transduction network that is active in cell division (Faesen et al, Nature (2017)). The crucial paradigm emerging from that study is that structural conversion of HORMA domains is catalysed, at both the assembly and the disassembly level, allowing dynamic control of signalling. In other words, controlling when and where HORMA domains use their unique interaction mechanism to create a signalling complex, essentially results in a signal in the right place and at the right time.

Why do we study this?
Our ultimate goal would be to reconstitute the dynamic control of the assembly and disassembly of HORMA-centric signalling complexes. While the previous work has provided us with detailed part lists, and has inspired possible wiring networks for the pathways involved, a mechanistic understanding of these processes in space and time has been lacking. Understanding these complex (bio)chemical reactions is vital to allow for future in vivo manipulations and is essential to interpret the perturbations that occur in disease.

What questions do we ask?
We are interested in understanding the molecular principles behind the extra-ordinary HORMA-based signalling. Many aspects of the assembly of signalling complexes by HORMA domains remain unclear. Chief among them is the mechanism for binding and exchange of protein partners. What are the interactions dynamics? What factors control the conformational switching of the HORMA domain? How is signalling initiated? How are targets selected?

How do we address those questions?
Biochemical reconstitution of dynamic biological processes is a powerful and widely applicable approach to unravel complex reactions and identify a minimal set of components and principles. Instead of studying these processes in their complex cellular environment, we aim to biochemically reconstitute these dynamic reactions from purified components in vitro. This allows us to study and manipulate all biochemical activities in great detail. Typically, our projects use a bottom-up approach, where we build macromolecular machines from scratch to understand them in detail using a combination of biochemical reconstitution, structural biology and biophysical investigations.

Further reading

  • Faesen AC#, Thanasoula M, Maffini S, Breit C, Müller F, van Gerwen S, Bange T, Musacchio A#. “Basis of catalytic assembly of the mitotic checkpoint complexNature (2017). # Co-corresponding author
  • Weir JR*, Faesen AC*, Klare K*, Basilico F, Fischböck, Pentakota S, Keller J, Petrovic A, Pesenti M, Vogt D, Wohlgemuth S, Herzog F, Musacchio A. “Insights from biochemical reconstitution into the architecture of human kinetochores” Nature (2016). * Equal contribution
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