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J Mol Biol. 1999 Nov 19;294(1):139-49.

The three-dimensional structure of the Limulus acrosomal process: a dynamic actin bundle.

Author information

1
National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030, USA.

Abstract

Limulus sperm contains a dynamic macromolecular structure that rapidly extends a 50 microm process called the true discharge. The core of this structure is a bundle of ordered filaments composed of a complex of actin, scruin and calmodulin. We determined its structure by electron crystallographic reconstruction. The three-dimensional map reveals an actin-scruin helix that is azimuthally modulated by the influence of the interactions of a filament with its neighbors. There are a variety of density connections with neighboring filaments involving scruin. Scruin commonly contacts one neighbor, but we observe up to three interfilament connections involving both domains of the 28 scruin molecules in the unit cell. Our structure indicates that promiscuous scruin-scruin contacts are the major determinants of bundle stability in the true discharge. It also suggests that rearrangements would be permitted, which can facilitate the transition from the coiled to the true discharge form.

PMID:
10556034
DOI:
10.1006/jmbi.1999.3222
[Indexed for MEDLINE]

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