Signal Peptide Requirements for Lymphocytic Choriomeningitis Virus Glycoprotein C Maturation and Virus Infectivity

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Abstract
Insertion of the lymphocytic choriomeningitis virus (LCMV) precursor glycoprotein C (GP-C) into the membrane of the endoplasmic reticulum is mediated by an unusual signal peptide (SP GP-C ). It is comprised of 58 amino acid residues and contains an extended hydrophilic N-terminal region, two hydrophobic regions, and a short C-terminal region. After cleavage by signal peptidase, SP GP-C accumulates in cells and virus particles. In the present study, we identified the LCMV SP GP-C as being an essential component of the GP complex and show that the different regions of SP GP-C are required for distinct steps in GP maturation and virus infectivity. More specifically, we show that one hydrophobic region of SP GP-C is sufficient for the membrane insertion of GP-C, while both hydrophobic regions are required for the processing and cell surface expression of the GPs. The N-terminal region of SP GP-C , on the other hand, is essential for pseudoviral infection of target cells. Furthermore, we show that unmyristoylated SP GP-C exposes its N-terminal region to the exoplasmic side. This SP GP-C can promote GP-C maturation but is defective in pseudoviral infection. Myristoylation and topology of SP GP-C in the membrane may thus hold the key to an understanding of the role of SP GP-C in GP-C complex maturation and LCMV infectivity.