Myosin 19 is Anchored to the Mitochondria, Affecting its Localization and Morphology

Mitochondria undergo continuous cycles of fission and fusion creating a highly dynamic network, which is essential for its proper functions in apoptosis, ATP generation and calcium homeostasis. Mitochondria long-range motility relies on the microtubule motors kinesin and dynein. Recently, actin and myosin 19 have been implicated in mitochondrial motility in vertebrates. However, the interaction of endogenous myosin 19 with the mitochondria remains unknown. Here, we show using multiple complementary approaches that endogenous myosin 19 is anchored directly to the outer mitochondrial membrane (OMM) in a monotopic fashion. We have identified a region of 30 residues at the tail domain of myosin 19, which is both essential and sufficient for myosin 19-OMM interaction. Furthermore, we have purified to near homogeneity a 45 long peptide comprised of this region to study its biochemical and biophysical properties. We performed in-vitro binding assay by fluorescence anisotropy of this specific purified peptide to vesicles with different phospholipid compositions. Our results revealed that that this peptide binds to vesicles mimicking the OMM with the highest affinity. To relate this tight binding to the mitochondria to myosin 19 ATPase activity, we have purified myosin 19-3IQ construct and measured its actin-dependent steady state ATPase activity. Interestingly, we found that it is completely inhibited by very low calcium concentration, suggesting that myosin 19 activity may be regulated by local calcium concentration. The interaction between a motor protein and an organelle, and the calcium dependence implicates that myosin 19 plays a role in mitochondria network dynamics.