Squid p196, a new member of the myosin-V class of motor proteins, is associated with motile axoplasmic organelles.
Axoplasmic organelles obtained from the squid giant axon move on actin filaments at an average velocity of 1 microm/s [Nature 356 (1992) 722]. The unconventional myosins, in particular, the myosin-V class of motor proteins, represent the most likely candidates to have a role in this motility. Experiments were performed to determine whether a member of the myosin-V class of unconventional myosins is present in axoplasm and optic lobes. Western blots of axoplasm probed with an affinity purified antibody to chicken brain myosin-V (CBM-V) showed cross-reactivity with a protein of Mr 196 kD (p196) which was subsequently purified from squid optic lobes using a modification of a protocol for the purification of CBM-V [Methods Enzymol. 298 (1998) 3; Cell 75 (1993) 215]. Western blots of CBM-V probed with an alpha-p196 polyclonal IgG showed cross-reactivity with CBM-V. Purified p196 has been found to be a calmodulin (CaM) binding protein that possesses calcium-stimulated actin-activated ATPase activity. Equilibrium density fractionation of motile axoplasmic organelle preparations has revealed that p196 cosedimented with the peak organelle fraction into Percoll gradients in the presence of cytochalasin B and ATP. Based on this evidence, we conclude that the p196 present in axoplasm and purified from optic lobes is a squid homolog of CBM-V and functions as a motor for fast transport of membranous organelles on actin filaments in neurons.
Cohen
D L
DL
Department of Biological Sciences, Dartmouth College, Hanover, NH 03755-3576, USA. dlcohen10@aol.com
D000199:Actins / Q000737:chemistry; D000251:Adenosine Triphosphatases / Q000737:chemistry; D000818:Animals; D001370:Axonal Transport / Q000502:physiology*; D001369:Axons / Q000737:chemistry* / Q000648:ultrastructure; D002148:Calmodulin-Binding Proteins / Q000032:analysis*; D002490:Central Nervous System / Q000737:chemistry / Q000648:ultrastructure; D002645:Chickens / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry*; D049832:Decapodiformes / Q000378:metabolism; D020409:Molecular Motor Proteins / Q000737:chemistry*; D018994:Myosin Light Chains / Q000032:analysis; D024701:Myosin Type V; D009419:Nerve Tissue Proteins / Q000032:analysis*; D015388:Organelles / Q000737:chemistry* / Q000648:ultrastructure; D022161:Transport Vesicles / Q000737:chemistry
D000199:Actins; D002148:Calmodulin-Binding Proteins; D020409:Molecular Motor Proteins; D018994:Myosin Light Chains; D009419:Nerve Tissue Proteins; C078829:chicken brain myosin-V p190; D000251:Adenosine Triphosphatases; D024701:Myosin Type V