How complement molecules kill bacteria

Project Information

ComBact

Grant agreement ID: 639209

DOI

10.3030/639209

Project closed

EC signature date 13 February 2015

Start date 1 March 2015

End date 29 February 2020

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 497 290,00

EU contribution

€ 1 497 290,00

Coordinated by

UNIVERSITAIR MEDISCH CENTRUM UTRECHT
Netherlands

Periodic Reporting for period 4 - ComBact (How complement molecules kill bacteria)

Reporting period: 2019-09-01 to 2020-02-29

Summary of the context and overall objectives of the project

Problem/issue
Antibiotic-resistant bacteria form a serious threat for public health and novel treatment strategies are needed urgently. One way to achieve this is to improve the activity of our immune system via therapeutic antibodies or vaccination. However, such developments are severely hampered by the lack of mechanistic insights into anti-bacterial immune mechanisms.

Overall objective
This grant aimed to unravel the molecular mechanisms underlying bacterial killing by the human immune system. In particular, we investigate the molecular functioning of the complement system, a large protein network in plasma that plays an essential role in the immune response against all invading bacteria. Complement rapidly labels bacteria for phagocytosis by immune cells and directly kills Gram-negative bacteria via pore formation (Membrane Attack Complex (MAC)). Within the ERC project, we aimed to provide insight on how Gram-negative bacteria are directly killed by complement.

Main conclusions of the action
*We unraveled crucial mechanisms of MAC-mediated killing of Gram-negatives:
-that convertase enzymes are crucial for localized assembly of MAC pores
-that MAC collaborates with antibiotics and components of the immune system
*We published a patent showing that Antibody engineering can be used to improve complement-dependent killing of bacteria
*We established novel methodologies to study C5 convertases and killing of bacteria by MAC
*We established novel methods to measure how antimicrobial components lyse the different cell compartments of Gram-negative bacteria

Importance for society
A better understanding of complement will improve desired complement activation by therapeutic antibodies and vaccination strategies in infectious diseases. Furthermore, our studies will create new avenues for blocking the undesired complement activation during systemic bacterial infections and sepsis.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

"The aim of this ERC project is to provide insight into the molecular events necessary for bacterial killing by the complement system.
Major achievements of this project are:

Objective 1 (understand C5 convertase biology):
*We established novel methodologies to study C5 convertases (project publication #1,42)
*We obtained insights into mechanisms of C5 convertase inhibition (project publication #42)
*We published a patent showing that Antibody engineering can be used to improve complement-dependent killing of bacteria (project patent #1)

Objective 2 (Determine the role of C5 convertases in MAC assembly and insertion on bacteria):
-We unraveled crucial mechanisms of MAC-mediated killing of Gram-negatives (project publication #39,43,69)
-that convertase enzymes are crucial for localized assembly of MAC pores (project publication #43, 69)

Objective 3. Elucidate how the MAC kills bacteria:
*We identified different steps in the permeabilization of composite bacterial cell envelopes (project publication #43, 69)
-that MAC collaborates with antibiotics (project publication #45)
-Unique collaboration with MAC and immune cells (project publication #68)

In all, we made major scientific and technological achievements.
Our results were disseminated through peer-reviewed publications, one patent, and several (oral and poster) presentations on international conferences.
Our findings that antibiotics can collaborate with the immune system (#45) yielded a lot of media attention, including an article in a renowed dutch newspaper (Heesterbeek) and a live interview on dutch radio (Heesterbeek and Rooijakkers).
In 2019, paper #43 was awarded for ‘best first PhD paper’ at the Scientific Spring Meeting of the Dutch Society of Microbiology (NVMM & KNVM).
In 2020, the thesis of Dani Heesterbeek was selected as winner for the 'best thesis' in the category General Microbiology (Dutch Society of Microbiology (NVMM & KNVM)).
I was selected for the prestigious EMBO Young Investigator Programme
(http://www.embo.org/news/press-releases/2016/twenty-five-life-scientists-join-embo-young-investigator-network)"

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

By the end of this project we obtained unique biochemical insights into C5 convertases and greatly enhanced understanding of how the Membrane Attack Complex kills bacterial cells.

Cover of thesis Heesterbeek and AFM images of MAC pores on bacterial membranes