Apparently, formation of both E1 homodimers and -trimers is somewhat reduced in a C171S mutant

Apparently, formation of both E1 homodimers and -trimers is somewhat reduced in a C171S mutant. the recovery of infectious viruses, proving that C123 in E1 and C295 in E2 play an essential role in the BVDV life cycle, and further support the conclusion that heterodimer formation is the crucial step. Interestingly, we found that the retention signal of E1 is mandatory for intracellular IDO-IN-12 localization of the heterodimer, so that absence of the E1 retention signal directs the heterodimer to the cell surface even though the E2 retention signal is still present. The covalent linkage between E1 and E2 plays an essential role for this process. were originally believed to only infect pigs and ruminants where IDO-IN-12 they induce a variety of clinical manifestations in farm or wild animals. Even though several good vaccines against the most important pestiviruses have been developed and a series of strict bio-safety measures like quarantine and stamping-out strategies have long been carried out, pestiviruses cause severe financial losses in the animal farming industry [2,3,4,5]. More recent studies revealed the existence of a variety of exotic pestiviruses with a much broader host range, leading to a new classification scheme [6,7]. Three envelope proteins, Erns, E1, and TNFSF10 E2, are present on the pestiviral particle [8,9]. E1 is by far the least characterized component of the virion with neither structure nor function analyzed in detail so far. The molecular size of glycosylated E1 is 27C33 kDa, depending on the virus species. This is only about half the size of E2. The glycoprotein E1 of the closely related HCV was shown to form non-covalently linked trimers on the virion, which are of functional importance [10]. Both Erns and E2 of pestiviruses can form homodimers that are found in infected cells and virions [8,11,12,13]. Because of the absence of robustly reacting specific antibodies against E1, it is still unknown whether E1 of pestiviruses forms oligomers or not. E1 forms disulfide linked heterodimers with E2 [8], and this structure was suggested to be important for pestivirus IDO-IN-12 infection since absence of heterodimers prevented infectivity of vesicular stomatitis viruses pseudotyped with bovine viral diarrhea virus (BVDV) envelope proteins E1 and E2 [14]. This publication reported that two positively charged residues in the E1 membrane anchor play a role in heterodimer formation since replacement of these residues by alanine reduced the amount of heterodimer. In addition, the cysteine residue at position 668 in the polyprotein (residue 171 in E1) was claimed to be not essential [14]. Similarly, for HCV, it has been shown that the charged residues within the transmembrane domains IDO-IN-12 of glycoproteins E1 and E2 play IDO-IN-12 an important role in E1/E2 heterodimerization [15,16]. However, the interaction between HCV E1 and E2 in infected cells is non-covalent, and, therefore, the interaction mechanism of HCV E1 and E2 can be hypothesized to be different from that of pestiviruses. So far, experimental data are missing that could reveal which cysteines of E1 and E2 of pestiviruses play essential roles in E1/E2 heterodimer formation. Crystal structure investigation of BVDV E2 showed that, except for the cysteine residue at position 295 in E2, all the other cysteines of E2 formed intramolecular disulfide bonds [17,18]. Accordingly, C295 is the only free cysteine residue in E2, which makes this site the logical candidate for the necessary disulfide linkage in dimers. Convincing experimental evidence is also missing that could clarify which of the E1 cysteines is involved in E1/E2 heterodimer formation. It was suggested that C171 in E1 forms a disulfide bond with C295 in E2, based on the results of computational secondary structure predictions and E1/E2 sequence alignments [19], along with the geometric constraints imposed by the recently published crystal structure of BVDV E2 [17,18]. In addition, other cysteine residues in E1 have been proposed to be engaged in heterodimer formation with E2 [20]. It is strongly suggested that amino acids important for.