title: Three-dimensional structure of the acrosomal filament of Limulus sperm by 400 kV electron cryomicroscopy.
abstract: The acrosomal bundle of Limulus sperm was imaged by electron cryomicroscopy, and the three-dimensional structure of a filament computationally isolated from the bundle was determined by helical image reconstruction. The actin model of Holmes was fit into the map, and its interactions with scruin, the actin-binding and cross-linking protein, were studied. Scruin binds to two consecutive actins along the helix via subdomains 1 and 3. These interactions involve helix-loop-beta motifs that are present in both actin subdomains (in different monomers) in positions available for binding by the same scruin molecule as it wraps around the actin. Taking first the structural motif homology and then looking for sequence pattern similarities, a stretch of 12 out of 20 matches in hydrophobicity is found. Scruin itself has been found to have an internal tandem homology.
authors.affiliation: Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: M F
authors.initials: MF
authors.lastname: Schmid
authors.forename: J
authors.initials: J
authors.lastname: Jakana
authors.forename: P
authors.initials: P
authors.lastname: Matsudaira
authors.forename: W
authors.initials: W
authors.lastname: Chiu
mesh_terms: D000177:Acrosome / Q000737:chemistry* / Q000648:ultrastructure*; D000199:Actins / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D000595:Amino Acid Sequence; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D005615:Freezing; D006737:Horseshoe Crabs / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D007091:Image Processing, Computer-Assisted; D008297:Male; D008854:Microscopy, Electron / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation
chemical_list: D000199:Actins; C083765:scruin protein, Horseshoe Crab