Regulation of Dictyostelium Myosin I and II

Dictyostelium expresses 12 different myosins, including seven single-headed myosins I and one conventional two-headed myosin II. In this review we foc us on the signaling pathways that regulate Dictyostelium myosin I and myosi n II. Activation of myosin I is catalyzed by a Cdc42/Rac-stimulated myosin I heavy chain kinase that is a member of the p21-activated kinase (PAK) fam ily. Evidence that myosin I is linked to the Arp2/3 complex suggests that p athways that regulate myosin I may also influence actin filament assembly. Myosin II activity is stimulated by a cGMP-activated myosin light chain kin ase and inhibited by myosin heavy chain kinases (MHCKs) that block bipolar filament assembly. Known MHCKs include MHCK A and MHCK B, which have a nove l type of kinase catalytic domain joined to a WD repeat domain, and MHC-pro tein kinase C (PKC), which contains both diacylglycerol kinase and PKC-rela ted protein kinase catalytic domains. A Dictyostelium PAK (PAKa) acts indir ectly to promote myosin II filament formation. suggesting that the MHCKs ma y be indirectly regulated by Rac GTPases. (C) 2001 Elsevier Science B.V. Al l rights reserved.