High homology between a trophoblastic protein (trophoblastin) isolated from ovine embryo and alpha-interferons

Ovine trophoblastic protein B (oTPB), an embryonic protein, is a 20 kDa secretory protein which is synthesized by the ovine conceptus from days 12 to 22 of pregnancy. oTPB was purified by HPLC using ion-exchange chromatography on a DEAE column and was subsequently chromatographed on a reversed-phase column. Automated Edman degradation was then used to determine the N-terminal amino acid sequence up to 45 residues. The sequence data reveal a significant homology between oTPB and bovine interferons alpha of class II: 64% of the amino acids are identical and 75% are homologous. A highly conserved region including residues 23-44 exhibits 82% homology. Identity between oTPB and either HuIFN-alpha.9 or MuIFN alpha.1 is 55%. These alignments between oTPB and IFNs occur at the N-terminus of the mature proteins and proceed without deletion. These results suggest that oTPB is an embryonic interferon.