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Cdc6 protein obstructs apoptosome assembly and consequent cell death by forming stable complexes with activated Apaf-1 molecules.

ABSTRACT: Cdc6 is the bifunctional AAA+ ATPase that assembles prereplicative complexes on origins of replication and activates p21(CIP1)- or p27(KIP1)-bound Cdk2. During the G(1)-S transition, the Cdc6 gene essential for chromosomal replication is activated by the E2F transcriptional factor. Paradoxically, Apaf-1 encoding the central component of the apoptosome is also activated at the same time and by E2F. Consequently, genes for antipodal life and death are regulated in the same manner by the same transcriptional factor. Here we report a striking solution to this paradox. Besides performing prereplicative complex assembly and Cdk2 activation, Cdc6 obstructed apoptosome assembly by forming stable complexes very likely with a monomer of cytochrome c-activated Apaf-1 molecules. This function depended on its own ATPase domain but not on the cyclin-binding motif. In proliferating rodent fibroblasts, Cdc6 continued to block apoptosome assembly induced by a non-cytochrome c or some other mechanism, suppressing seemingly unintended apoptosis when promoting cell proliferation. Thus, Cdc6 is an AAA+ ATPase with three functions, all working for life.

SUBMITTER: Niimi S

PROVIDER: S-EPMC3365716 | biostudies-literature | 2012 May

REPOSITORIES: biostudies-literature

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Cdc6 protein obstructs apoptosome assembly and consequent cell death by forming stable complexes with activated Apaf-1 molecules.

Niimi Shinichiro S Arakawa-Takeuchi Shiho S Uranbileg Baasanjav B Park Jun-ha JH Jinno Shigeki S Okayama Hiroto H

The Journal of biological chemistry 20120406 22

Cdc6 is the bifunctional AAA+ ATPase that assembles prereplicative complexes on origins of replication and activates p21(CIP1)- or p27(KIP1)-bound Cdk2. During the G(1)-S transition, the Cdc6 gene essential for chromosomal replication is activated by the E2F transcriptional factor. Paradoxically, Apaf-1 encoding the central component of the apoptosome is also activated at the same time and by E2F. Consequently, genes for antipodal life and death are regulated in the same manner by the same trans ...[more]

PMID: 22493447

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Project description:BackgroundBinding of cytochrome c, released from the damaged mitochondria, to the apoptotic protease activating factor 1 (Apaf-1) is a key event in the apoptotic signaling cascade. The binding triggers a major domain rearrangement in Apaf-1, which leads to oligomerization of Apaf-1/cytochrome c complexes into an apoptosome. Despite the availability of crystal structures of cytochrome c and Apaf-1 and cryo-electron microscopy models of the entire apoptosome, the binding mode of cytochrome c to Apaf-1, as well as the nature of the amino acid residues of Apaf-1 involved remain obscure.ResultsWe investigated the interaction between cytochrome c and Apaf-1 by combining several modeling approaches. We have applied protein-protein docking and energy minimization, evaluated the resulting models of the Apaf-1/cytochrome c complex, and carried out a further analysis by means of molecular dynamics simulations. We ended up with a single model structure where all the lysine residues of cytochrome c that are known as functionally-relevant were involved in forming salt bridges with acidic residues of Apaf-1. This model has revealed three distinctive bifurcated salt bridges, each involving a single lysine residue of cytochrome c and two neighboring acidic resides of Apaf-1. Salt bridge-forming amino acids of Apaf-1 showed a clear evolutionary pattern within Metazoa, with pairs of acidic residues of Apaf-1, involved in bifurcated salt bridges, reaching their highest numbers in the sequences of vertebrates, in which the cytochrome c-mediated mechanism of apoptosome formation seems to be typical.ConclusionsThe reported model of an Apaf-1/cytochrome c complex provides insights in the nature of protein-protein interactions which are hard to observe in crystallographic or electron microscopy studies. Bifurcated salt bridges can be expected to be stronger than simple salt bridges, and their formation might promote the conformational change of Apaf-1, leading to the formation of an apoptosome. Combination of structural and sequence analyses provides hints on the evolution of the cytochrome c-mediated apoptosis.

Dataset Information

Cdc6 protein obstructs apoptosome assembly and consequent cell death by forming stable complexes with activated Apaf-1 molecules.

Publications

Cdc6 protein obstructs apoptosome assembly and consequent cell death by forming stable complexes with activated Apaf-1 molecules.

Similar Datasets

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