During activation of the Limulus sperm acrosomal process, actin filaments undergo a change in twist that is linked with the conversion from a coiled to a straight scruin-actin bundle. Since scruin had not been purified, its identity as an actin-binding protein has not been demonstrated. Using HECAMEG (methyl-6-O-(N-heptylcarbamoyl)--D-glucopyranoside) detergent extraction in concert with high calcium, we purified native scruin and identified it as an equimolar complex with calmodulin. I-Calmodulin overlays and calmodulin-Sepharose indicate that scruin binds calmodulin in calcium but not in EGTA. Overlay experiments also map the calmodulin binding site between the putative N- and C-terminal -propeller domains within residues 425-446. Immunofluorescence microscopy reveals that calmodulin colocalizes with scruin and actin in the coiled bundle. Although scruin binds calmodulin, pelleting assays and electron microscopy show that the scruin cross-links F-actin into bundles independently of calcium. Based on our biochemical and structural studies, we suggest a model to explain how scruin controls a change in twist of actin filaments during the acrosome reaction. We predict that calcium subtly alters scruin conformation through its calmodulin subunit and the conformation change in scruin causes a shift in the relative positions of the scruin-bound actin subunits.

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				J. H. Shin, L. Mahadevan, G. S. Waller, K. Langsetmo, and P. Matsudaira Stored elastic energy powers the 60-{micro}m extension of the Limulus polyphemus sperm actin bundle J. Cell Biol., September 29, 2003; 162(7): 1183 - 1188. [Abstract] [Full Text] [PDF]

				Y. Miyagawa, H. Tanaka, N. Iguchi, K. Kitamura, Y. Nakamura, T. Takahashi, K. Matsumiya, A. Okuyama, and Y. Nishimune Molecular cloning and characterization of the human orthologue of male germ cell-specific actin capping protein {alpha}3 (cp{alpha}3) Mol. Hum. Reprod., June 1, 2002; 8(6): 531 - 539. [Abstract] [Full Text] [PDF]

				R. J. Kelso, A. M. Hudson, and L. Cooley Drosophila Kelch regulates actin organization via Src64-dependent tyrosine phosphorylation J. Cell Biol., February 18, 2002; 156(4): 703 - 713. [Abstract] [Full Text] [PDF]

				G. M. Guild, P. S. Connelly, K. A. Vranich, M. K. Shaw, and L. G. Tilney Actin filament turnover removes bundles from Drosophila bristle cells J. Cell Sci., January 2, 2002; 115(3): 641 - 653. [Abstract] [Full Text] [PDF]

				C. Lécuyer, J.-L. Dacheux, E. Hermand, E. Mazeman, J. Rousseaux, and R. Rousseaux-Prévost Actin-Binding Properties and Colocalization with Actin During Spermiogenesis of Mammalian Sperm Calicin Biol Reprod, December 1, 2000; 63(6): 1801 - 1810. [Abstract] [Full Text]

				V. Aidinis, D. C. Dias, C. A. Gomez, D. Bhattacharyya, E. Spanopoulou, and S. Santagata Definition of Minimal Domains of Interaction Within the Recombination-Activating Genes 1 and 2 Recombinase Complex J. Immunol., June 1, 2000; 164(11): 5826 - 5832. [Abstract] [Full Text] [PDF]

				R. P. Johnson and S. W. Craig Actin Activates a Cryptic Dimerization Potential of the Vinculin Tail Domain J. Biol. Chem., January 7, 2000; 275(1): 95 - 105. [Abstract] [Full Text] [PDF]

				S Grieshaber and N. Petersen The Drosophila forked protein induces the formation of actin fiber bundles in vertebrate cells J. Cell Sci., January 7, 1999; 112(13): 2203 - 2211. [Abstract] [PDF]

				J. Philips and I. Herskowitz Identification of Kel1p, a Kelch Domain-containing Protein Involved in Cell Fusion and Morphology in Saccharomyces cerevisiae J. Cell Biol., October 19, 1998; 143(2): 375 - 389. [Abstract] [Full Text] [PDF]

				W. J. Kranewitter, J. Ylanne, and M. Gimona UNC-87 Is an Actin-bundling Protein J. Biol. Chem., February 23, 2001; 276(9): 6306 - 6312. [Abstract] [Full Text] [PDF]

				R. J. Kelso, A. M. Hudson, and L. Cooley Drosophila Kelch regulates actin organization via Src64-dependent tyrosine phosphorylation J. Cell Biol., February 18, 2002; 156(4): 703 - 713. [Abstract] [Full Text] [PDF]