title: Polylysine induces an antiparallel actin dimer that nucleates filament assembly: crystal structure at 3.5-A resolution.
abstract: An antiparallel actin dimer has been proposed to be an intermediate species during actin filament nucleation. We now show that latrunculin A, a marine natural product that inhibits actin polymerization, arrests polylysine-induced nucleation at the level of an antiparallel dimer, resulting in its accumulation. These dimers, when composed of pyrene-labeled actin subunits, give rise to a fluorescent excimer, permitting detection during polymerization in vitro. We report the crystallographic structure of the polylysine-actin-latrunculin A complex at 3.5-A resolution. The non-crystallographic contact is consistent with a dimeric structure and confirms the antiparallel orientation of its subunits. The crystallographic contacts reveal that the mobile DNase I binding loop of one subunit of a symmetry-related antiparallel actin dimer is partially stabilized in the interface between the two subunits of a second antiparallel dimer. These results provide a potential explanation for the paradoxical nucleation of actin filaments that have exclusively parallel subunits by a dimer containing antiparallel subunits.
authors.affiliation: Research Service, Malcom Randall Department of Veterans Affairs Medical Center and the University of Florida College of Medicine, Gainesville, Florida 32608, USA. bubbmr@medicine.ufl.edu
authors.forename: Michael R
authors.initials: MR
authors.lastname: Bubb
authors.forename: Lakshmanan
authors.initials: L
authors.lastname: Govindasamy
authors.forename: Elena G
authors.initials: EG
authors.lastname: Yarmola
authors.forename: Sergey M
authors.initials: SM
authors.lastname: Vorobiev
authors.forename: Steven C
authors.initials: SC
authors.lastname: Almo
authors.forename: Thayumanasamy
authors.initials: T
authors.lastname: Somasundaram
authors.forename: Michael S
authors.initials: MS
authors.lastname: Chapman
authors.forename: Mavis
authors.initials: M
authors.lastname: Agbandje-McKenna
authors.forename: Robert
authors.initials: R
authors.lastname: McKenna
mesh_terms: D000199:Actins / Q000096:biosynthesis* / Q000737:chemistry; D000818:Animals; D018360:Crystallography, X-Ray; D019281:Dimerization; D008958:Models, Molecular; D011107:Polylysine / Q000737:chemistry / Q000502:physiology*; D011487:Protein Conformation; D011817:Rabbits
chemical_list: D000199:Actins; D011107:Polylysine