title: Inhibition of eukaryotic translation elongation by the antitumor natural product Mycalamide B.
abstract: Mycalamide B (MycB) is a marine sponge-derived natural product with potent antitumor activity. Although it has been shown to inhibit protein synthesis, the molecular mechanism of action by MycB remains incompletely understood. We verified the inhibition of translation elongation by in vitro HCV IRES dual luciferase assays, ribosome assembly, and in vivo [(35)S]methinione labeling experiments. Similar to cycloheximide (CHX), MycB inhibits translation elongation through blockade of eEF2-mediated translocation without affecting the eEF1A-mediated loading of tRNA onto the ribosome, AUG recognition, or dipeptide synthesis. Using chemical footprinting, we identified the MycB binding site proximal to the C3993 28S rRNA residue on the large ribosomal subunit. However, there are also subtle, but significant differences in the detailed mechanisms of action of MycB and CHX. First, MycB arrests the ribosome on the mRNA one codon ahead of CHX. Second, MycB specifically blocked tRNA binding to the E-site of the large ribosomal subunit. Moreover, they display different polysome profiles in vivo. Together, these observations shed new light on the mechanism of inhibition of translation elongation by MycB.
authors.affiliation: Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Dang
authors.forename: Tilman
authors.initials: T
authors.lastname: Schneider-Poetsch
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Eyler
authors.forename: John C
authors.initials: JC
authors.lastname: Jewett
authors.forename: Shridhar
authors.initials: S
authors.lastname: Bhat
authors.forename: Viresh H
authors.initials: VH
authors.lastname: Rawal
authors.forename: Rachel
authors.initials: R
authors.lastname: Green
authors.forename: Jun O
authors.initials: JO
authors.lastname: Liu
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D001688:Biological Products / Q000737:chemistry / Q000494:pharmacology*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D006801:Humans; D010441:Peptide Chain Elongation, Translational / Q000187:drug effects*; D011714:Pyrans / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D001688:Biological Products; D011714:Pyrans; C059647:mycalamide B