Polylysine induces an antiparallel actin dimer that nucleates filament assembly: crystal structure at 3.5-A resolution.
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.
Bubb
Michael R
MR
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
Govindasamy
Lakshmanan
L
Yarmola
Elena G
EG
Vorobiev
Sergey M
SM
Almo
Steven C
SC
Somasundaram
Thayumanasamy
T
Chapman
Michael S
MS
Agbandje-McKenna
Mavis
M
McKenna
Robert
R
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
D000199:Actins; D011107:Polylysine