title: Regulatory role of the second gelsolin-like domain of Caenorhabditis elegans gelsolin-like protein 1 (GSNL-1) in its calcium-dependent conformation and actin-regulatory activities.
abstract: Caenorhabditis elegans gelsolin-like protein-1 (GSNL-1) is an unconventional member of the gelsolin family of actin-regulatory proteins. Unlike typical gelsolin-related proteins with three or six G domains, GSNL-1 has four gelsolin-like (G) domains (G1-G4) and exhibits calcium-dependent actin filament severing and capping activities. The first G domain (G1) of GSNL-1 is necessary for its actin-regulatory activities. However, how other domains in GSNL-1 participate in regulation of its functions is not understood. Here, we report biochemical evidence that the second G domain (G2) of GSNL-1 has a regulatory role in its calcium-dependent conformation and actin-regulatory activities. Comparison of the sequences of gelsolin-related proteins from various species indicates that sequences of G2 are highly conserved. Among the conserved residues in G2, we focused on D162 of GSNL-1, since equivalent residues in gelsolin and severin are part of the calcium-binding sites and is a pathogenic mutation site in human gelsolin causing familial amyloidosis, Finish-type. The D162N mutation does not alter the inactive and fully calcium-activated states of GSNL-1 for actin filament severing (at 20 nM GSNL-1) and capping activities (at 50 nM GSNL-1). However, under these conditions, the mutant shows reduced calcium sensitivity for activation. By contrast, the D162N mutation strongly enhances susceptibility of GSNL-1 to chymotrypsin digestion only at high calcium concentrations but not at low calcium concentrations. The mutation also reduces affinity of GSNL-1 with actin monomers. These results suggest that G2 of GSNL-1 functions as a regulatory domain for its calcium-dependent actin-regulatory activities by mediating conformational changes of the GSNL-1 molecule.
authors.affiliation: Department of Pathology, Emory University, Atlanta, Georgia 30322, USA.
authors.forename: Zhongmei
authors.initials: Z
authors.lastname: Liu
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Ono
mesh_terms: D000199:Actins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D052139:Intracellular Calcium-Sensing Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed
chemical_list: D000199:Actins; D029742:Caenorhabditis elegans Proteins; C532447:GSNL-1 protein, C elegans; D052139:Intracellular Calcium-Sensing Proteins; D002118:Calcium