Journal
JOURNAL OF VIROLOGY
Volume 78, Issue 15, Pages 7894-7903Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/JVI.78.15.7894-7903.2004
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Funding
- NCI NIH HHS [CA90636, R01 CA090636] Funding Source: Medline
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The trimeric fusion (F) glycoproteins of morbilliviruses are activated by furin cleavage of the precursor F, into the F-1 and F-2 subunits. Here we show that an additional membrane-proximal cleavage occurs and modulates F protein function. We initially observed that the ectodomain of approximately one in three measles virus (MV) F proteins is cleaved proximal to the membrane. Processing occurs after cleavage activation of the precursor F-0 into the F-1 and F-2 subunits, producing F-1a and F-1b fragments that are incorporated in viral particles. We also detected the F-1b fragment, including the transmembrane domain and cytoplasmic tail, in cells expressing the canine distemper virus (CDV) or mumps virus F protein. Six membrane-proximal amino acids are necessary for efficient CDV F-1a/b cleavage. These six amino acids can be exchanged with the corresponding MV F protein residues of different sequence without compromising function. Thus, structural elements of different sequence are functionally exchangeable. Finally, we showed that the alteration of a block of membrane-proximal amino acids results in diminished fusion activity in the context of a recombinant CDV. We envisage that selective loss of the membrane anchor in the external subunits of circularly arranged F protein trimers may disengage them from pulling the membrane centrifugally, thereby facilitating fusion pore formation.
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