title: Apoptosis induction by Bid requires unconventional ubiquitination and degradation of its N-terminal fragment.
abstract: Bcl-2 family member Bid is subject to autoinhibition; in the absence of stimuli, its N-terminal region sequesters the proapoptotic Bcl-2 homology 3 (BH3) domain. Upon proteolytic cleavage in its unstructured loop, Bid is activated, although structural data reveal no apparent resulting conformational change. We found that, upon Bid cleavage, the N-terminal fragment (tBid-N) is ubiquitinated and degraded, thus freeing the BH3 domain in the C-terminal fragment (tBid-C). Ubiquitination of tBid-N is unconventional because acceptor sites are neither lysines nor the N terminus. Chemical approaches implicated thioester and hydroxyester linkage of ubiquitin and mutagenesis implicated serine and possibly threonine as acceptor residues in addition to cysteine. Acceptor sites reside predominantly but not exclusively in helix 1, which is required for ubiquitination and degradation of tBid-N. Rescue of tBid-N from degradation blocked Bid's ability to induce mitochondrial outer membrane permeability but not mitochondrial translocation of the cleaved complex. We conclude that unconventional ubiquitination and proteasome-dependent degradation of tBid-N is required to unleash the proapoptotic activity of tBid-C.
authors.affiliation: Division of Immunology, The Netherlands Cancer Institute, 1066 CX Amsterdam, Netherlands.
authors.forename: Stephen W G
authors.initials: SW
authors.lastname: Tait
authors.forename: Evert
authors.initials: E
authors.lastname: de Vries
authors.forename: Chiel
authors.initials: C
authors.lastname: Maas
authors.forename: Anna M
authors.initials: AM
authors.lastname: Keller
authors.forename: Clive S
authors.initials: CS
authors.lastname: D'Santos
authors.forename: Jannie
authors.initials: J
authors.lastname: Borst
mesh_terms: D000595:Amino Acid Sequence / Q000502:physiology; D000596:Amino Acids / Q000502:physiology; D017209:Apoptosis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein / Q000737:chemistry / Q000378:metabolism*; D045744:Cell Line, Tumor; D006367:HeLa Cells; D006801:Humans; D053078:Membrane Potential, Mitochondrial / Q000502:physiology; D051336:Mitochondrial Membranes / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D017433:Protein Structure, Secondary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology*
chemical_list: D000596:Amino Acids; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D025801:Ubiquitin; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex