Antibodies (immunoglobulins; IgG) are some of the most important molecules of our immune
defense against pathogens and tumor cells. These Y-shaped proteins recognize and tightly bind
specific structures on the surface of viruses, bacteria and tumor cells via their two "arms", the so-
called Fab regions, and thus mark them for destruction by the immune system. This is possible
because the stem of the Y-shaped antibody, the so-called Fc region, then protrudes from the surface
of the target cell, and other molecules of the immune system, in particular components of the
classical complement pathway, can recognize it. If everything goes right, these molecules bind to the
Fc region and to each other, ultimately causing the perforation of the cell membrane thus the
elimination of the antibody-tagged target cell.
There are four different subclasses of IgG antibodies (IgG1 - IgG4) in our blood that differ mainly in
the length and flexibility of the so-called `hinge` region (the joint that connects the Fab and Fc regions
in the center of the Y). In this project, we will investigate how exactly these IgG subclasses induce the
elimination of target cells. Of particular interest is whether a recently discovered mechanism that
allows IgG1 molecules to arrange themselves into antibody-hexamers (snowflake-like structures of
six Y-shaped antibodies each) after binding to a target cell also applies to the other subclasses (IgG2,
IgG3 and IgG4). Hexamerization represents a decisive step in the activation of the classical
complement pathway for IgG1, and we will study whether this is the case for the other subclasses as
well. In addition, we will elucidate further potential influences on the successful activation of the
complement system, such as the binding strength between antibody and target cell and differences
in antibody glycosylation (the type of attached sugar molecules).
We will employ a combination of several high-end microscopy techniques (high-speed atomic force
microscopy, single-molecule fluorescence microscopy) as well as techniques for quantifying the
interactions between antibodies, cell membranes and complement proteins (single-molecule force
spectroscopy and quartz-crystal microbalance), which together will allow us to decipher these
processes both structurally and dynamically.
The project is carried out by Dr. Johannes Preiner (project leader) in cooperation with Dr. Jaroslaw
Jacak at the University of Applied Sciences Upper Austria, Department of Medical Technology,
Campus Linz.