The long and short of mitochondrial fusion

Mitochondria malfunction unless they occasionally fuse with each other. Papers by Song et al. (page 749) and Griparic et al. (page 757) now elucidate the protein processing necessary for these mergers and pin down one of the responsible enzymes.

A protein matchmaker that promotes mitochondrial unions is OPA1, which is located in the organelle's inner membrane. The protein is faulty in dominant optic atrophy, an inherited form of blindness. OPA1's many varieties—there are eight mRNA splice variants, each of which encodes polypeptides that undergo further processing—fall into two categories: long and short. Yeast harbor a similar protein and require both lengths for fusion. But a previous study suggested that only the long form is responsible for mitochondrial...