title: Crystalline actin tubes. I. Is the conformation of the lanthanide-induced actin tube monomer more like F-actin than G-actin?
abstract: Actin, isolated from rabbit skeletal muscle, forms highly-ordered aggregates when it binds six moles of the lanthanide ion, Gd3+. In the presence of 0.1 M KCl, these aggregates are referred to as actin tubes. The monomer contained in the repeating subunit of these tubes possess a number of functional characteristics which include: (i) binding to myosin or subfragment-1 of myosin; (ii) rapid conversion into filamentous Gd-actin which can activate myosin ATPase activity; (iii) a slow rate of exchange of the bound nucleotide; (iv) a slow rate of exchange of the metal cation; (v) a resistance to digestion by proteolytic enzymes. Additionally, the monomer of the Gd-actin tube structures appears to stoichiometrically bind ATP and exhibit a lower minimum protein concentration for tube formation than is needed for the formation of F-actin. The properties listed above suggest that the actin monomer, which comprises the Gd-actin tubes, bears little resemblance to either the G-actin monomer or the recently-described actin monomer conformation that exists under conditions that favour polymerization. The data suggest that the actin molecules which comprise the Gd-actin tube structures contain sites which bind myosin, nucleotide and metal cations and that these sites are similar to the sites on F-actin.
mesh_terms: D000199:Actins / Q000032:analysis / Q000378:metabolism*; D000227:Adenine Nucleotides / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D008674:Metals, Rare Earth / Q000378:metabolism / Q000494:pharmacology*; D009132:Muscles / Q000378:metabolism / Q000648:ultrastructure*; D009218:Myosins / Q000378:metabolism; D011487:Protein Conformation; D011817:Rabbits
chemical_list: D000199:Actins; D000227:Adenine Nucleotides; D008674:Metals, Rare Earth; D000251:Adenosine Triphosphatases; D009218:Myosins