Primary structure of the glycoprotein E2 of coronavirus MHV-A59 and identification of the trypsin cleavage site

Luytjes, Willem; Sturman, Lawrence S.; Bredenbee, Peter J.; Charite, Jeroen; van der Zeijst, Bernard A.M.; Horzinek, Marian C.; Spaan, Willy J.M.

Abstract The nucleotide sequence of the peplomer (E2) gene of MHV-A59 was determined from a set of overlapping cDNA clones. The E2 gene encodes a protein of 1324 amino acids including a hydrophobic signal peptide. A second large hydrophobic domain is found near the COOH terminus and probably represents the membrane anchor. Twenty glycosylation sites are predicted. Cleavage of the E2 protein results in two different 90K species, 90A and 90B (L. S. Sturman, C. S. Ricard, and K. V. Holmes (1985) J. Virol. 56, 904–911), and activates cell fusion. Protein sequencing of the trypsin-generated N-terminus revealed the position of the cleavage site. 90A and 90B could be identified as the C-terminal and the N-terminal parts, respectively. Amino acid sequence comparison of the A59 and 1HM E2 proteins showed extensive homology and revealed a stretch of 89 amino acids in the 90B region of the A59 E2 protein that is absent in JHM.