Role of the C-terminal tryptophan residue for the structure-function of the alphavirus capsid protein.
The Semliki Forest virus capsid protein is a multifunctional protein which packages genomic RNA into nucleocapsid structures and binds to viral spike protein during budding. In addition, the capsid protein has an autoproteolytic activity whereby the C-terminal tryptophan is used as the substrate for cotranslational cleavage of the viral structure polyprotein. The autoproteolytic domain of the capsid protein has a chymotrypsin-like fold but has two additional short beta-strands which place the tryptophan into the active site. Here, we have substituted the C-terminal tryptophan of Semliki Forest virus capsid protein for alanine, arginine and phenylalanine and analysed the effects on different functions of the C protein such as nucleocapsid formation, spike binding and autoproteolytic activity. We found that (i) tryptophan is a better substrate for the autoproteolytic activity, (ii) the wild-type tryptophan is the only residue that allows efficient viral growth and (iii) an aromatic residue is important for correct initial folding and stability of the protein.
Skoging
U
U
Microbiology and Tumorbiology Center, Karolinska Institute, Stockholm, S-171 77, Sweden.
Liljeström
P
P
D002213:Capsid / Q000737:chemistry* / Q000235:genetics; D009154:Mutation; D012672:Semliki forest virus / Q000737:chemistry*; D013329:Structure-Activity Relationship; D014364:Tryptophan
D014364:Tryptophan