title: Tropomyosin is a tetramer under physiological salt conditions.
abstract: Tropomyosin (TM) is a coiled-coil dimer of alpha-helical peptides, which self associates in a head- to-tail fashion along actin polymers, conferring stability to the microfilaments and serving a regulatory function in acto-myosin driven force generation. While the major amount of TM is associated with filaments also in non-muscle cells, it was recently reported that there are isoform-specific pools of TM multimers (not associated with F-actin), which appear to be utilized during actin polymerization and reformed during depolymerization. To determine the size of these multimers, skeletal muscle TM was studied under different salt conditions using gel-filtration and sucrose gradient sedimentation, and compared with purified non-muscle TM 1 and 5, as well as with TM present in non-muscle cell extracts and skeletal muscle TM added to such extracts. Under physiological salt conditions TM appears as a single homogenous peak with the Stokes radius 8.2 nm and the molecular weight (mw) 130,000. The corresponding values for TM 5 are 7.7 nm and 104,000, respectively. This equals four peptides, implying that native TM is a tetramer in physiological salt. It is therefore concluded that the TM multimers are tetramers.
authors.affiliation: Department of Cell Biology, The Wenner-Gren Institute, Stockholm University, Sweden. ingrid.lassing@wgi.su.se
authors.forename: Ingrid
authors.initials: I
authors.lastname: Lassing
authors.forename: Louise
authors.initials: L
authors.lastname: Hillberg
authors.forename: Anna-Stina
authors.initials: AS
authors.lastname: Höglund
authors.forename: Roger
authors.initials: R
authors.lastname: Karlsson
authors.forename: Clarence
authors.initials: C
authors.lastname: Schutt
authors.forename: Uno
authors.initials: U
authors.lastname: Lindberg
mesh_terms: D000199:Actins / Q000737:chemistry; D000818:Animals; D008970:Molecular Weight; D018482:Muscle, Skeletal / Q000378:metabolism; D009994:Osmolar Concentration; D020033:Protein Isoforms; D055503:Protein Multimerization; D011817:Rabbits; D014335:Tropomyosin / Q000737:chemistry* / Q000302:isolation & purification
chemical_list: D000199:Actins; D020033:Protein Isoforms; D014335:Tropomyosin