Biosynthesis, maturation, and acid activation of the Semliki Forest virus fusion protein

M. Kielian, S. Jungerwirth, K. Ullrich Sayad, S. DeCandido

Research output: Contribution to journalArticlepeer-review

69 Scopus citations


The Semliki Forest virus spike protein has a potent membrane fusion activity which is activated in vivo by the low pH of endocytic vacuoles. The spike protein is composed of two transmembrane subunits, E1 and E2, plus E3, a peripheral polypeptide. Acid-induced conformational changes in the E1 or E2 subunits were analyzed by using monoclonal antibodies specific for the acid-treated spike protein. E1 and E2 reacted with the antibodies after treatment of wild-type or mutant virus at the pH of fusion. The E1 conformational change resembled fusion in its requirement for both low pH and cholesterol. Pulse-chase analysis and intracellular pH treatment were then used to determine the ability of the newly synthesized spike to undergo acid-induced conformational changes. p62, the precursor to E2 and E3, was shown to undergo a pH-dependent conformational change similar to that of E2 and was sensitive to acid very soon after biosynthesis. In contrast, a posttranslational maturation event was required for the conversion of E1 to the pH-sensitive form. E1 maturation occurred fairly late in the exocytic pathway, after the virus spike had passed the medial Golgi but before incorporation of the spike into a new virus particle.

Original languageEnglish (US)
Pages (from-to)4614-4624
Number of pages11
JournalJournal of virology
Issue number10
StatePublished - 1990

ASJC Scopus subject areas

  • Microbiology
  • Immunology
  • Insect Science
  • Virology


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