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sequence of the molecule [14]. The peptides were used in competition assays with the native molecule.
Peptide inhibition of a particular function would implicate the region of the molecule that it represented
in the elicitation of that function. The effect of the IFN-τ peptides on the antiviral activity of ovine IFNτ
was examined in a dose/response assay using Madin Darby bovine kidney (MDBK) cells challenged
with vesicular stomatitis virus. The carboxy-terminal peptide oIFN-τ(139–172) was found to be the most
effective inhibitor of antiviral activity. Three additional peptides, oIFN-τ(1–37), (62–92), and
(119–150), also reduced IFN-τ antiviral activity. This suggested that multiple regions of the IFN-τ
molecule interact with the Type I IFN receptor and elicit antiviral activity. These regions are underlined
in Table 3. The data were consistent with studies of antiviral activity and receptor binding with IFN-α
analogs demonstrating that 3 distinct sites, located in the amino-terminal, internal, and carboxy-terminal
regions of the molecule, influenced human IFN-α activity [15].
To verify functional results using synthetic peptides, antipeptide antisera were produced [14]. All
antipeptide antisera were reactive with the native molecule. Interestingly, antisera titers correlated with
the hydropathic index of the peptide, rather than with the predicted surface accessibility of the specific
region in the 3-D configuration. Consistent with the peptide studies, antisera against the same four
regions of the molecule inhibited IFN-τ activity while antisera to other regions did not.
Since IFN-τ and IFN-α bind to the same receptor, the ability of the IFN-τ synthetic peptides to block
both bovine and human IFN-α was examined. Interestingly, only three of the four inhibitory peptides
were effective competitors of IFN-α. Cross-inhibition of IFN-α by the internal and carboxy-terminal
peptides was observed and suggested that these residues may adopt a similar conformation in both
molecules and bind to a common site on the receptor. The aminoterminal peptide failed to reduce IFN-α
function entirely. Thus, either the IFN-α amino-terminus has a much higher affinity for receptor or the
IFN-τ aminoterminus binds a unique site on the receptor complex that may be associated with its unique
properties. As expected, none of the peptides blocked the antiviral activity of IFN-τ, which interacts
with a different receptor.
Next, it was determined whether the same active regions of IFN-τ were involved in additional systems.
The Type I IFN receptor on cells has been reported to be somewhat more promiscuous than on other
cell types [16]; therefore, vesicular stomatitis challenge of Fc-9 cells was performed. Only the carboxyterminal
peptide inhibited IFN-τ activity in this system [17]. This suggested that it was the carboxyterminus
that was crucial to receptor interaction. In studies examining IFN-τ-treated feline
immunodeficiency virus infected FeT-1 cells and human immunodeficiency virus-infected peripheral
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