Crystallographic analysis of acrosomal bundle from Limulus sperm.
J Mol Biol
; 221(2): 711-25, 1991 Sep 20.
Article
em En
| MEDLINE
| ID: mdl-1920441
ABSTRACT
The acrosomal process of Limulus sperm contains a bundle of filaments composed of actin and a 102 kDa protein in a 11 molar ratio. The structure of the bundle in true discharge was investigated by electron cryomicroscopy, X-ray scattering and crystallographic image analysis. A bundle can be characterized as a quasi-crystal with continuously varying views along the bundle axis. Each segment of the bundle is found to obey the symmetry of space group P1, with a = b = 147 A, c = 762 A, alpha = 90 degrees, beta = 90.6 degrees, gamma = 120 degrees. A unit cell contains a helical repeat of the filament with a selection rule following that of an actin filament. A 24 A projection map based on the h0l view was reconstructed after averaging 5300 unit cells from six electron images. Filaments in this projection are well separated and clearly display a 21 screw symmetry. This screw symmetry results from the helical parameters of the bundle filament and is found to be a non-crystallographic symmetry element present in the unit cell. Our structural analysis has led to the proposal that the assembly of a stable bundle with a defined maximum diameter can be controlled by the crystallographic packing of the twisted filaments.
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Base de dados:
MEDLINE
Assunto principal:
Difração de Raios X
/
Acrossomo
/
Actinas
/
Caranguejos Ferradura
Limite:
Animals
Idioma:
En
Revista:
J Mol Biol
Ano de publicação:
1991
Tipo de documento:
Article