Structure, function, and regulation of myo1c

Abstract

Myo1c is the first mammalian single-headed myosin identified. Although the cellular function of myosin 1c is not clearly understood, there is evidence showing that myosin 1c is involved in insulin-mediated GLUT4 exocytosis. The N-terminal of myo1c is the motor domain responsible for actin-binding and ATP hydrolysis. The adjacent neck domain contains IQ motifs which bind to CaM. The C-terminal end contains a PH domain which can bind to plasma membranes. A suit of biochemistry experiments demonstrate that myo1c can bind 3 copies of calmodulin (CaM) in the absence of Ca²⁺. Our unpublished the X-ray crystal structure of the myo1c tail shows that the bindings between the first two IQ motifs and CaM follows the canonical CaM/IQ-motif binding mode, in which the N-lobe of CaM binds to C-terminus and the C-lobe of CaM binds to N-terminus of IQ-motif, respectively. Unexpectedly, the third IQ-motif of myo1c binds to CaM in a novel binding mode. Instead of binding to the C-terminal half of IQ3, the N-lobe of the CaM binds to a parallel two helix bundle immediately following IQ3. Static light scattering method and NMR spectroscopy were used to investigate how myo1c responds to Ca²⁺ binding. The data indicate that upon Ca²⁺ influx, myo1c bind to two CaM. Apo-CaM bound to IQ1 and IQ2 will dissociate upon Ca²⁺ concentration rises. The CaM which binds to IQ3 and postIQ will change its conformation upon Ca²⁺ concentration increases, and the IQ3 motif can engage both lobes of CaM. More interestingly, the postIQ motif becomes capable of binding to one molecular of Ca²⁺-CaM with high affinity. The results presented in this thesis will demonstrate that myo1c can undergo a significant Ca²⁺ mediated conformation changes via its light chain CaM.

Date of Award	2013
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology