Prohibitins: mitochondrial partners in development and stress response

Twelve years after their discovery in plants, prohibitins (PHBs) have retained their status as some of the most enigmatic mitochondrial proteins. Although the original hypothesis that PHBs act as negative cell cycle regulators has lost its impetus in plants, the essential molecular function(s) PHB complexes perform in the inner mitochondrial membrane are now beginning to be understood. We review the current state of knowledge to propose a unifying model that positions the PHB complex as a universal protein scaffold for key mitochondrial processes, including protein processing, respiratory chain function and mitochondrial DNA organization. Furthermore, recent findings indicate that PHBs play an active role in stress tolerance and are involved in triggering retrograde signals in response to stress and mitochondrial dysfunction.