Myosins pp 391-401 | Cite as

Class Ix Myosins

Negative Regulators of the Small GTP-binding Protein Rho
  • Martin BÄhler
Part of the Proteins and Cell Regulation book series (PROR, volume 7)


Class IX myosins are found in animals from invertebrates to vertebrates. Invertebrates contain a single myosin IX gene, whereas vertebrates contain two myosin IX genes, MYO9A and MYO9B. Mammalian Myo9b, the only class IX myosin studied so far, has unique motor properties. It is the first myosin for which ATP hydrolysis is the rate-limiting step in the chemical cycle and although it is a single-headed myosin, it can take multiple steps along F-actin before dissociating. Class IX myosins are motorized signaling molecules that contain in their tail domain a Rho GTPase-activating protein (GAP) activity. Mammalian members of myosin class IX negatively regulate the monomeric GTP-binding proteins RhoA-C. In cells, Myo9b accumulates in regions of active actin polymerization such as in extending lamellipodia. In these regions Myo9b might locally down regulate contractility and adhesion that are controlled by Rho activity and thereby contribute to sustained lamellipodial extension and cell polarity.


ATPase C1 domain IQ-motif myosin IX RhoGAP 


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Copyright information

© Springer 2008

Authors and Affiliations

  • Martin BÄhler
    • 1
  1. 1.Institut für Allgemeine Zoologie und GenetikWestfälische-Wilhelms UniversitätSchlossplatz 5Germany

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