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  • Title: Identification of sites for alkylation by N-ethylmaleimide and pertussis toxin-catalyzed ADP-ribosylation on GTP-binding proteins.
    Author: Hoshino S, Kikkawa S, Takahashi K, Itoh H, Kaziro Y, Kawasaki H, Suzuki K, Katada T, Ui M.
    Journal: FEBS Lett; 1990 Dec 10; 276(1-2):227-31. PubMed ID: 2125009.
    Abstract:
    An alpha beta gamma-trimeric GTP-binding protein (Go) serving as the substrate of pertussis toxin-(IAP) catalyzed ADP-ribosylation was purified from rat brain membranes. The constituent alpha-subunit (alpha o) was alkylated with N-ethylmaleimide (NEM), and the functionally important sulfhydryl groups were investigated. There were at least two cysteine residues highly reactive to NEM on the GDP-bound form of alpha o. These alkylations resulted in loss of its ability to be ADP-ribosylated by IAP and to associate with beta gamma, but leaving the GTP-binding site of alpha o intact. The reacted cysteine residues were identified by the sequencing of tryptic fragments of alpha o. One of the alkylation sites was Cys-351, which was four amino acid residues away from the carboxyl-terminus of the molecule. The Cys-351 was proven to be also a site for IAP-catalyzed ADP-ribosylation. Possible roles of cysteine residues on the alpha-subunit of Go are discussed in the functions of the signal transducing protein.
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