1. ¹INSERM, U848, Pavillion de Recherche 1, Villejuif, France
2. ²Institut Gustave Roussy, Villejuif, France
3. ³Faculté de Médecine – Université Paris-Sud XI, Villejuif, France
4. ⁴Lead generation, AstraZeneca R&D Mölndal, Pepparedsleden 1, Mölndal, Sweden
5. ⁵ImmunoGen Inc., Cambridge, MA, USA

Correspondence: Dr G Kroemer, INSERM U848, Pavillion de Recherche 1, Institut Gustave Roussy, PR1 39 rue Camille Desmoulins, F-94805 Villejuif, France. E-mail: kroemer@igr.fr

Received 11 December 2006; Revised 16 March 2007; Accepted 30 March 2007; Published online 14 May 2007.

Abstract

The viral mitochondrial inhibitor of apoptosis (vMIA) encoded by the human cytomegalovirus exerts cytopathic effects and neutralizes the proapoptotic endogenous Bcl-2 family member Bax by recruiting it to mitochondria, inducing its oligomerization and membrane insertion. Using a combination of computational modeling and mutational analyses, we addressed the structure–function relationship of the molecular interaction between the protein Bax and the viral antiapoptotic protein vMIA. We propose a model in which vMIA exhibits an overall fold similar to Bcl-X_L. In contrast to Bcl-X_L, however, this predicted conformation of vMIA does not bind to the BH3 domain of Bax and rather engages in electrostatic interactions that involve a stretch of amino acids between the BH3 and BH2 domains of Bax and an -helical domain located within the previously defined Bax-binding domain of vMIA, between the putative BH1-like and BH2-like domains. According to this model, vMIA is likely to bind Bax preferentially in its membrane-inserted conformation. The capacity of vMIA to cause fragmentation of the mitochondrial network and disorganization of the actin cytoskeleton is independent of its Bax-binding function. We found that 131–147 vMIA mutant, which lacks both the Bax-binding function and cell-death suppression but has intact mitochondria-targeting capacity, is similar to vMIA in its ability to disrupt the mitochondrial network and to disorganize the actin cytoskeleton. vMIA131–147 is a dominant-negative inhibitor of the antiapoptotic function of wild-type vMIA. Our experiments with vMIA131–147 suggest that vMIA forms homo-oligomers, which may engage in cooperative and/or multivalent interactions with Bax, leading to its functional neutralization.