title: Humanin binds and nullifies Bid activity by blocking its activation of Bax and Bak.
abstract: Recently, we discovered that Humanin (HN), a small endogenous peptide of 24 amino acids, binds to and inhibits the proapoptotic protein Bax. We show here that HN also interacts with the BH3-only Bcl-2/Bax family protein, Bid, as well as a truncated form of Bid (tBid) associated with protease-mediated activation of this proapoptotic protein. Synthetic HN peptide binds purified Bid and tBid in vitro and blocks tBid-induced release of cytochrome c and SMAC from isolated mitochondria, whereas mutant peptides that fail to bind Bid or tBid lack this activity. Moreover, HN peptide also retained protective activity on bax-/-mitochondria, indicating that HN can block tBid-induced release of apoptogenic proteins from these organelles in a Bax-independent manner. HN peptide inhibits tBid-induced oligomerization of Bax and Bak in mitochondrial membranes, as shown by experiments with chemical cross-linkers or gel filtration. Gene transfection experiments showed that HN (but not an inactive mutant of HN) also protects intact cells from apoptosis induced by overexpression of tBid. We conclude that Bid represents an additional cellular target of HN, and we propose that HN-mediated suppression of Bid contributes to the antiapoptotic activity of this endogenous peptide.
authors.affiliation: Burnham Institute, La Jolla, California 92037, USA.
authors.forename: Dayong
authors.initials: D
authors.lastname: Zhai
authors.forename: Frederic
authors.initials: F
authors.lastname: Luciano
authors.forename: Xiuwen
authors.initials: X
authors.lastname: Zhu
authors.forename: Bin
authors.initials: B
authors.lastname: Guo
authors.forename: Arnold C
authors.initials: AC
authors.lastname: Satterthwait
authors.forename: John C
authors.initials: JC
authors.lastname: Reed
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D013329:Structure-Activity Relationship; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
chemical_list: C494772:BAK1 protein, human; C494826:BAX protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494773:Bak1 protein, mouse; C494827:Bax protein, mouse; C494815:Bid protein, mouse; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D010455:Peptides; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; C427211:humanin; C015462:polyarginine