title: Polymerization, three-dimensional structure and mechanical properties of Ddictyostelium versus rabbit muscle actin filaments.
abstract: To assess more systematically functional differences among non-muscle and muscle actins and the effect of specific mutations on their function, we compared actin from Dictyostelium discoideum (D-actin) with actin from rabbit skeletal muscle (R-actin) with respect to the formation of filaments, their three-dimensional structure and mechanical properties. With Mg(2+) occupying the single high-affinity divalent cation-binding site, the course of polymerization is very similar for the two types of actin. In contrast, when Ca(2+ )is bound, D-actin exhibits a significantly longer lag phase at the onset of polymerization than R-actin. Crossover spacing and helical screw angle of negatively stained filaments are similar for D and R-F-actin filaments, irrespective of the tightly bound divalent cation. However, three-dimensional helical reconstructions reveal that the intersubunit contacts along the two long-pitch helical strands of D-(Ca)F-actin filaments are more tenuous compared to those in R-(Ca)F-actin filaments. D-(Mg)F-actin filaments on the other hand exhibit more massive contacts between the two long-pitch helical strands than R-(Mg)F-actin filaments. Moreover, in contrast to the structure of R-F-actin filaments which is not significantly modulated by the divalent cation, the intersubunit contacts both along and between the two long-pitch helical strands are weaker in D-(Ca)F-actin compared to D-(Mg)F-actin filaments. Consistent with these structural differences, D-(Ca)F-actin filaments were significantly more flexible than D-(Mg)F-actin. Taken together, this work documents that despite being highly conserved, muscle and non-muscle actins exhibit subtle differences in terms of their polymerization behavior, and the three-dimensional structure and mechanical properties of their F-actin filaments which, in turn, may account for their functional diversity.
authors.affiliation: M.E. Müller Institute for Structural Biology, University of Basel, Klingelbergstrasse 70, Biozentrum, CH-4056, Basel, Switzerland.
authors.forename: M O
authors.initials: MO
authors.lastname: Steinmetz
authors.forename: A
authors.initials: A
authors.lastname: Hoenger
authors.forename: D
authors.initials: D
authors.lastname: Stoffler
authors.forename: A A
authors.initials: AA
authors.lastname: Noegel
authors.forename: U
authors.initials: U
authors.lastname: Aebi
authors.forename: C A
authors.initials: CA
authors.lastname: Schoenenberger
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D000199:Actins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D001665:Binding Sites; D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002413:Cations, Divalent / Q000378:metabolism / Q000494:pharmacology; D004023:Dictyostelium / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D005453:Fluorescence; D005682:Gadolinium / Q000494:pharmacology; D007091:Image Processing, Computer-Assisted; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D008854:Microscopy, Electron; D008958:Models, Molecular; D018482:Muscle, Skeletal / Q000737:chemistry; D009154:Mutation / Q000235:genetics; D009994:Osmolar Concentration; D018583:Pliability / Q000187:drug effects; D011110:Polymorphism, Genetic / Q000235:genetics; D011189:Potassium Chloride / Q000494:pharmacology; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D020836:Protein Structure, Quaternary / Q000187:drug effects; D011721:Pyrenes / Q000378:metabolism; D011817:Rabbits
chemical_list: D000199:Actins; D001704:Biopolymers; D002413:Cations, Divalent; D020033:Protein Isoforms; D011721:Pyrenes; D011189:Potassium Chloride; C030984:pyrene; D005682:Gadolinium; D008274:Magnesium; D002118:Calcium