André Eißmann


A1 Molecular function regulating the interaction of the of the HIV-1 regulatory virus protein R (Vpr) with host cells

Principal investigator
Ulrich Schubert

Jutta Eichler

PhD exam: 21.12.2010

Chemical Chaperones Support HIV-1 Budding

“Chemical chaperones”, a class of structurally unrelated substances of low molecular weight and good water solubility, are able to control the synthesis and function of proteins in vivo. They efficiently equilibrate across cellular membranes, where they influence the thermodynamic properties of proteins by regulating the hydration of exposed polypeptide backbones and side chains of partially unfolded structures. They function, at least in part, by reducing the amount of structurally bound water at protein surfaces and ultimately stabilize the preferred folding state of a protein by enhancing intra-molecular interactions.
Glycerol, one of the most prominent members of the chemical chaperones, in sub-toxic concentrations increases the release of viral particles from HIV-1 producing cells. In addition to pulse-chase experiments, western blot virus-release kinetic studies, conducted in a variety of HIV-1 infected or transfected cells, revealed that the ATP-independent protein stabilizing effect of glycerol overcomes the arrest of virus release induced by either proteasome shut down or the mutation of virus encoded budding factors. Although the nature of the underlying mechanism(s) of this phenomenon is still unknown, it further supports the role of protein folding in virus assembly and release.

Figure: The crucial role of chaperones in protein turn over and their consequences in viral budding. During protein synthesis folding intermediates are folded into their functional quaternary structure via the assistance of chaperones. The resulting native proteins are finally able to achieve their assignment, in the case of HIV: to accomplish assembly, budding, and maturation of progeny viruses.
Because of the imperfection of protein synthesis approximately 30% of translated proteins are misfolded, displaying so called “Defective Ribosomal Products” (DRiPs), which were recycled by the Ubiquitin-Proteasome-System. A small amount of these misfolded intermediates escapes proteasomal degradation and accumulates into the cell. This “death end” confirmation´s abundance can artificially be enlarged by blocking the proteasomes function. In the end these Gag-DRiPs might act in a prion-like manner to prevent the action of functional proteins resulting in stalked virus-like particles unable to bud from cell surface completely. Altogether this scheme illustrates the points of taking influence on viral budding either using chemical chaperones, their specific inhibitors or proteasome inhibitors.



Röder, R., Bruns, K., Sharma, A., Eissmann, A., Hahn, F., Studtrucker, N., Fossen, T., Wray, V., Henklein, P. and Schubert, U. (2008). Synthesis of full length PB1-F2 influenza A virus proteins from 'Spanish flu' and 'bird flu'. J Pept Sci 14, 954-962.

Bruns, K., Studtrucker, N., Sharma, A., Fossen, T., Mitzner, D., Eissmann, A., Tessmer, U., Röder, R., Henklein, P., Wray, V. and Schubert, U. (2006). Structural characterization and oligomerization of PB1-F2, a proapoptotic influenza A virus protein. J Biol Chem 282, 353-363.



September 2009 First Annual Retreat, Erlangen School of Molecular Communication, Schloss Atzelsberg, Atzelsberg, Germany
The role of Protein folding in HIV-1 Replication”
March 2009 19th Annual Meeting of the Society of Virology. Leipzig, Germany
"The role of chaperones in HIV-1 replication"
March 2008 18th Annual Meeting of the Society of Virology. Heidelberg, Germany
"Phosphorylation of the influenza A virus PB1-F2 protein by PKC is required for efficient virus propagation"
September 2007 3rd European Congress of Virology. Nuremberg, Germany
"Structural characterization and oligomerization of PB1-F2, a proapoptotic influenza A virus protein"
September 2006 Symposium: Regulators of Adaptive Immunity  
"Structure, folding, and oligomerization of PB1-F2, a pro-apoptotic influenza A virus protein."
March 2006 16th Annual Meeting of the Society of Virology. Munich, Germany
"The ubiquitin ligase POSH regulates HIV-1 budding"