Crystal structure of the tegument protein UL82 (pp71) from human cytomegalovirus.

Human cytomegalovirus (HCMV) is an opportunistic pathogen that infects a majority of the world population. It may cause severe disease in immunocompromised people and lead to pregnancy loss or grave disabilities of the fetus upon congenital infection. For effective replication and lifelong persistence in its host, HCMV relies on diverse functions of its tegument protein UL82, also known as pp71. Up to now, little is known about the molecular mechanisms underlying the multiple functions of this crucial viral protein. Here, we describe the X-ray structure of full-length UL82 to a resolution of 2.7 Å. A single polypeptide chain of 559 amino acids mainly folds into three ß-barrels. We show that UL82 forms a dimer in the crystal as well as in solution. We identify point mutations that disturb the dimerization interface and show that the mutant protein is monomeric in solution and upon expression in human cells. On the basis of the three-dimensional structure, we identify structural homologs of UL82 from other herpesviruses and analyze whether their functions are preserved in UL82. We demonstrate that UL82, despite its structural homology to viral deoxyuridinetriphosphatases (dUTPases), does not possess dUTPase activity. Prompted by the structural homology of UL82 to the ORF10 protein of murine herpesvirus 68 (MHV68), which is known to interact with the RNA export factor ribonucleic acid export 1 (Rae1), we performed coimmunoprecipitations and demonstrated that UL82 indeed interacts with Rae1. This suggests that HCMV UL82 may play a role in mRNA export from the nucleus similar to ORF10 encoded by the gammaherpesviruses MHV68.

Biological function of Dictyocaulus viviparus asparaginyl peptidase legumain-1 and its suitability as a vaccine target.

The present study characterized the biological function of the asparaginyl peptidase legumain-1 (LEG-1) of the bovine lungworm Dictyocaulus viviparus and its suitability as a recombinant vaccine against dictyocaulosis. Quantitative real-time PCR and immunoblot analysis revealed LEG-1 to be almost exclusively transcribed and expressed in parasitic lungworm stages. Immunohistochemistry localized the enzyme in the parasite's gut, which was confirmed by immunoblots detecting LEG-1 in the gut as well as male testes. LEG-1 was recombinantly (rLEG-1) expressed in the yeast Pichia pastoris and subsequently analysed in activity assays for its enzyme functions and substrate specificity. For sufficient functionality, rLEG-1 needed trans-activation through D. viviparus cathepsin L-2, indicating a novel mechanism of legumain activation. After trans-activation, rLEG-1 worked best at pH 5·5 and 35-39 °C and cleaved a legumain-specific artificial substrate as well as the natural substrates bovine collagen types I and II. In a clinical vaccination trial, rLEG-1 did not protect against challenge infection. Results of in vitro characterization, transcription pattern and localization enhance the presumption that LEG-1 participates in digestion processes of D. viviparus. Since rLEG-1 needs trans-activation through a cathepsin, it is probably involved in an enzyme cascade and therefore remains interesting as a candidate in a multi-component vaccine.