A novel zinc-binding domain is essential for formation of the functional Junín virus envelope glycoprotein complex.
The envelope glycoprotein of the Junín arenavirus (GP-C) mediates entry into target cells through a pH-dependent membrane fusion mechanism. Unlike other class I viral fusion proteins, the mature GP-C complex retains a cleaved, 58-amino-acid signal peptide (SSP) as an essential subunit, required both for trafficking of GP-C to the cell surface and for the activation of membrane fusion. SSP has been shown to associate noncovalently in GP-C via the cytoplasmic domain (CTD) of the transmembrane fusion subunit G2. In this report we investigate the molecular basis for this intersubunit interaction. We identify an invariant series of six cysteine and histidine residues in the CTD of G2 that is essential for incorporation of SSP in the GP-C complex. Moreover, we show that a CTD peptide fragment containing His-447, His-449, and Cys-455 specifically binds Zn(2+) at subnanomolar concentrations. Together, these results suggest a zinc finger-like domain structure in the CTD of G2. We propose that the remaining residues in the series (His-459, Cys-467, and Cys-469) form an intersubunit zinc-binding center that incorporates Cys-57 of SSP. This unusual motif may act to retain SSP in the GP-C complex and position the ectodomain loop of SSP for its role in modulating membrane fusion activity. The unique tripartite organization of GP-C could provide novel molecular targets for therapeutic intervention in arenaviral disease.
York
Joanne
J
Montana Biotechnology Center, The University of Montana, Science Complex, Room 221, Missoula, MT 59812, USA.
Nunberg
Jack H
JH
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002522:Chlorocebus aethiops; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D018051:Junin virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008561:Membrane Fusion; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals; D014709:Vero Cells; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014760:Viral Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism*; D016335:Zinc Fingers / Q000235:genetics
D006023:Glycoproteins; D021382:Protein Sorting Signals; D014759:Viral Envelope Proteins; D014760:Viral Fusion Proteins; D015032:Zinc