Abstract
On the assumption that dephosphorylation of the neurotropic coronavirus JHM (JHMV) nucleocapsid protein (N) may be connected with initiation of the infectious cycle we searched for a relevant host enzyme activity. Analysis of subcellular fractions from L‐2 murine fibroblasts, separated by dual Percoll density gradients, revealed the presence of a phosphoprotein phosphatase (PPPase), co‐sedimenting with the endososomal/prelysosomal material, which possesses high activity against N. With purified [22P]N as substrate it was demonstrated that this PPPase, distinguishable from acid and alkaline phosphatases, acts optimally at neutral pH in the presence of Mn2+ following treatment with a detergent. Complete inhibition with okadaic acid at 0.9–4.5 μM but not at 1–10 nM relegates this PPase to a type I protein phosphatase. Similar PPPase activity for N was present in the endosome fraction of a rat Roc‐1 astrocytoma‐oligodendrocyte cell line and in homogenates of brain and cultured oligodendrocytes. Our data suggest that the phosphorylated N of the inoculum may be modified by the endosomal PPPase in host cells, including those from the CNS so as to facilitate the JHMV infectious process.
Keywords: Phosphoprotein phosphatase; Endosome; Coronavirus; Nucleocapsid protein; EDTA; Ethylenediaminetetraacetate, disodium salt; EGTA; Ethyleneglycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid; PMSF; phenyl methyl sulfonyl fluoride; pNPP; p-nitrophenyl phosphate
Mohandas Devaki V. and Dales Samuel(1991), Endosomal association of a protein phosphatase with high dephosphorylating activity against a coronavirus nucleocapsid protein, FEBS Letters, 282, doi: 10.1016/0014-5793(91)80528-B
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