title: Role of tropomodulin's leucine rich repeat domain in the formation of neurite-like processes.
abstract: Actin dynamics is fundamental for neurite development; monomer depolymerization from pointed ends is rate-limiting in actin treadmilling. Tropomodulins (Tmod) make up a family of actin pointed end-capping proteins. Of the four known isoforms, Tmod1-Tmod3 are expressed in brain cells. We investigated the role of Tmod's C-terminal (LRR) domain in the formation of neurite-like processes by overexpressing Tmod1 and Tmod2 with deleted or mutated LRR domains in PC12 cells, a model system used to study neuritogenesis. Tmod1 overexpression results in a normal quantity and a normal length of processes, while Tmod2 overexpression reduces both measures. The Tmod2 overexpression phenotype is mimicked by overexpression of Tmod1 with the LRR domain removed or with three point mutations in the LRR domain that disrupt exposed clusters of conserved residues. Removal of Tmod2's LRR domain does not significantly alter the outgrowth of neurite-like processes compared to that of Tmod2. Overexpression of chimeras with the N-terminal and C-terminal domains switched between Tmod1 and Tmod2 reinforces the idea that Tmod1's LRR domain counteracts the reductive effect of the Tmod N-terminal domain upon formation of processes while Tmod2's LRR domain does not. We suggest that the TM-dependent actin capping ability of both Tmods inhibits the formation of processes, but in Tmod1, this inhibition can be controlled via its LRR domain. Circular dichroism, limited proteolysis, and molecular dynamics demonstrate structural differences in the C-terminal region of the LRR domains of Tmod1, Tmod2, and the Tmod1 mutant.
authors.affiliation: Cellular and Molecular Synaptic Function Unit, OIST Graduate University , 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan.
authors.forename: Laurent
authors.initials: L
authors.lastname: Guillaud
authors.forename: Kevin T
authors.initials: KT
authors.lastname: Gray
authors.forename: Natalia
authors.initials: N
authors.lastname: Moroz
authors.forename: Caroline
authors.initials: C
authors.lastname: Pantazis
authors.forename: Edward
authors.initials: E
authors.lastname: Pate
authors.forename: Alla S
authors.initials: AS
authors.lastname: Kostyukova
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002942:Circular Dichroism; D007930:Leucine / Q000378:metabolism; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D009154:Mutation; D016501:Neurites / Q000378:metabolism*; D016716:PC12 Cells; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D051348:Tropomodulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; C495831:Tmod1 protein, mouse; C495834:Tmod2 protein, mouse; D051348:Tropomodulin; D007930:Leucine
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