title: A carboxy-terminal fragment of protein mu 1/mu 1C is present in infectious subvirion particles of mammalian reoviruses and is proposed to have a role in penetration.
abstract: Penetration of a cell membrane as an early event in infection of cells by mammalian reoviruses appears to require a particular type of viral particle, the infectious subvirion particle (ISVP), which is generated from an intact virion by proteolytic cleavage of the outer capsid proteins sigma 3 and mu 1/mu 1C. Characterizations of the structural components and properties of ISVPs are thus relevant to attempts to understand the mechanism of penetration by reoviruses. In this study, a novel, approximately 13-kDa carboxy-terminal fragment (given the name phi) was found to be generated from protein mu 1/mu 1C during in vitro treatments of virions with trypsin or chymotrypsin to yield ISVPs. With trypsin treatment, both the carboxy-terminal fragment phi and the amino-terminal fragment mu 1 delta/delta were shown to be generated and to remain attached to ISVPs in stoichiometric quantities. Sites of protease cleavage were identified in the deduced amino acid sequence of mu 1 by determining the amino-terminal sequences of phi proteins: trypsin cleaves between arginine 584 and isoleucine 585, and chymotrypsin cleaves between tyrosine 581 and glycine 582. Findings in this study indicate that sequences in the phi portion of mu 1/mu 1C may participate in the unique functions attributed to ISVPs. Notably, the delta-phi cleavage junction was predicted to be flanked by a pair of long amphipathic alpha-helices. These amphipathic alpha-helices, together with the myristoyl group at the extreme amino terminus of mu 1/mu 1N, are proposed to interact directly with the lipid bilayer of a cell membrane during penetration by mammalian reoviruses.
authors.affiliation: Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts.
authors.forename: M L
authors.initials: ML
authors.lastname: Nibert
authors.forename: B N
authors.initials: BN
authors.lastname: Fields
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002213:Capsid / Q000032:analysis*; D002918:Chymotrypsin / Q000494:pharmacology; D007526:Isoelectric Point; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000032:analysis*; D011487:Protein Conformation; D012087:Reoviridae / Q000737:chemistry* / Q000254:growth & development; D012088:Reoviridae Infections / Q000378:metabolism*; D014357:Trypsin / Q000494:pharmacology; D014771:Virion / Q000737:chemistry* / Q000187:drug effects / Q000254:growth & development; D014779:Virus Replication
chemical_list: D010446:Peptide Fragments; D002918:Chymotrypsin; D014357:Trypsin