Structure and function


Session organizers: Piet Gros and Péter Gál


The topics:

A.) Structure of a complement serine protease (MASP-1) and its inhibitor (C1-inhibitor)


Required reading:

1.) Dobó, J., Harmat, V., Beinrohr, L., Sebestyén, E., Závodszky, P. and Gál, P. (2009) MASP-1, a promiscuous complement protease: structure of its catalytic region reveals the basis of its broad specificity

J. Immunol. 183, 1207-1214

2.) Beinrohr, L., Harmat, V., Dobó, J., Lőrincz, Zs., Gál, P., and Závodszky, P. (2007)

C1 inhibitor serpin domain structure reveals the likely mechanism of heparin potentiation and conformational disease

J. Biol. Chem. 282, 21100-21109

Questions to be discussed:

1.) What is the advantage of determining the structure of recombinant protein molecules over the native molecules. What are the expression systems that are routinely used for expression proteins to be crystallized? What problems can the glycosylation cause?

2.) In which characteristics is MASP-1 different form a typical complement serine protease (e.g. C1r, C1s, MASP-2, Factor D)? How can the structure help us to explain the unusual characteristics of MASP-1?

3.) Although the overall structure of the serine protease domain of MASP-1 resembles to that of trypsin, MASP-1 is a much less efficient protease than trypsin. How can the structure explain this phenomenon?

4.) What is the general mode of action of a serpin type serine protease inhibitor. What is the difference between the active and latent forms of serpins?

5.) How can the structure of C1-inhibitor help us in explaining the pathogenesis of the disease hereditary angioedema?

6.) Heparin and other polyanions can modulate the serpin-protease interactions. Which characteristic of the structure of C1-inhibitor is crucial to understand this phenomenon?

7.) What do you think about the possibility of application of polyanions in the clinical practice as anti-complement agents?


B. Molecular mechanisms of convertase activity and regulation

Required reading:


2. Rooijakkers, Wu et al. Nat. Immunology 2009  SUPPLEMENTARY MATERIAL

3. Wu et al. Nat Immunology 2009  SUPPLEMENTARY MATERIAL

Questions to be discussed:

- Structures are now known for C3b, Factor B and their complexes.

What do these data imply for convertase formation?

- What does the stabilized convertase structure imply for the convertase activity and complement amplification?

- What differences do you expect between the classical and alternative pathway C3 convertases? Can you speculate what the C5 convertase may look like?

- The structure of the convertase was stabilized by an immune evasion molecule SCIN from S. aureus. How is complement activiation evaded by S. aureus by SCIN? What other mechanisms may be used by pathogens to block complement amplification?

- What does the structure of FH domains 1-4 in complex with C3b imply for the regulatory function of complete FH?

- The authors present "general models" for the decay-accelerating activity and cofactor activity. How general are these models and what differences may we expect between the different regulators?

- How are the various 20 domains of FH involved in recognition of host cells and in decay accelerating activity and cofactor activity; and how can we use this information to design therapeutic proteins with specific recognition and function?