TBK1 and optic nerve disorder: Of relevance to a discussion of the role of mitochondria in optic neuropathies, the activity of OPTN as a linker protein is enhanced by being phosphorylated by TANK-Binding Kinase 1 (TBK1), which increases both ubiquitin-OPTN binding affinity [27] and OPTN-LC3 binding affinity [28].