Protein Shaped Like a Spider: Immune Protein C4BP Is Potentially Suitable as a Transporter for Drugs

The protein C4BP is similar to a spider in its spatial form with eight "arms." The structure of the "spider body" has recently been described in detail by researchers from the Helmholtz Centre for Infection Research (HZI) in Braunschweig and the Technische Universität Darmstadt. This leads the scientists to unconventional ideas -- the protein is possibly suitable as a scaffold for the transport of active pharmaceutical substances, particularly biomolecules.

The so-called complement system is a part of the innate immune defence within the human body: more than sixty different proteins form one of the first countermeasures against invading pathogens. One of them is the C4b binding protein known as C4BP. It is involved in the immune defence against bacteria in the blood.

Scientists found out that it has eight "arms" and thus resembles a spider to a certain degree. Seven of the "arms" are identical as "alpha chains," while the eighth, a "beta chain" is different from the others. The spider body that holds these side chains together is called the oligomerisation domain. Its structure was of special interest to researchers, since it determines the spatial alignment of the "arms."

C4BP is quite stable. Even boiling is not able to break down its form. Usually, human proteins remain stable up to about 40°C. Higher temperatures are of course not found in the body, but the stability of C4BP has a completely different purpose: As is the case with all components of the complement system, the C4b binding protein is present in blood plasma. The proteins are exposed to enormous shear forces in the blood stream. Therefore, the protein needs a high stability in order to be able to withstand these forces.