Defects in the mitochondrial respiratory chain are the most common mitochondrial disorders in humans and are often caused by defects in the assembly machinery of the complexes. These disorders result in several human diseases, however the mechanism of disease for many conditions is not yet fully understood.

The assembly of the respiratory chain complexes involves the coordination of a large number of mitochondrial and nuclear encoded subunits, which are assembled into mature complexes by a highly regulated assembly machinery. A number of respiratory complex accessory subunits (subunits not involved in the complex’s core catalytic function), and assembly factors (proteins involved in complex I assembly but not found in the mature complex) have been found to be mutated in mitochondrial diseases, however the exact function of these proteins still remains largely unknown.

Using recently developed tools for genome editing, we are constructing knockout cell lines for proteins implicated in respiratory complex assembly in cultured human cells. We make use of transcription activator-like effector nucleases (TALENs), which act as site-specific “molecular scissors”, generating small and targeted genomic deletions. The examination of these cell lines give us new and important knowledge into the biogenesis of human respiratory complexes, and reveal the role of specific subunits that are mutated in mitochondrial disease.