Biol Reprod Keystone Symposia Conference on Frontiers in Reproductive Biology & Regulation of Fertility.
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BOR - Papers in Press, published online ahead of print October 4, 2002.
Biol Reprod 2002, 10.1095/biolreprod.102.004093
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Biology of Reproduction 67, 1936-1942 (2002)
DOI: 10.1095/biolreprod.102.004093 © 2002 Society for the Study of Reproduction, Inc.

Gamete Biology

Sperm PP1{gamma}2 Is Regulated by a Homologue of the Yeast Protein Phosphatase Binding Protein sds221

Zaohua Huanga, Balwant Khatrab, Mathieu Bollenc, Daniel W. Carrd, and Srinivasan Vijayaraghavan2,a

a Biological Sciences Department, Kent State University, Kent, Ohio 44242 b California State University, Long Beach, California 90840 c Faculteit Geneeskunde, Katholieke Universiteit Leuven, Leuven, Belgium d Veterans Affairs Medical Center, Oregon Health Sciences University, Portland, Oregon 97201

Serine/threonine phosphatase PP1{gamma}2 is a testis-specific protein phosphatase isoform in spermatozoa. This enzyme appears to play a key role in motility initiation and stimulation. Catalytic activity of PP1{gamma}2 is higher in immotile compared with motile spermatozoa. Inhibition of PP1{gamma}2 activity causes both motility initiation and motility stimulation. Protein phosphatases, in general, are regulated by their binding proteins. The objective of this article is to understand the mechanisms by which PP1{gamma}2 is regulated, first by identifying its regulatory proteins. We had previously shown that a portion of bovine sperm PP1{gamma}2 is present in the cytosolic fraction of sperm sonicates. We purified PP1{gamma}2 from soluble bovine sperm extracts by immunoaffinity chromatography. Gel electrophoresis of the purified enzyme showed that it was complexed to a protein 43 Mr x 10-3 in size. Microsequencing revealed that this protein is a mammalian homologue of sds22, which is a yeast PP1 binding protein. Phosphatase activity measurements showed that PP1{gamma}2 complexed to sds22 is catalytically inactive. The complex cannot be activated by limited proteolysis. The complex is unable to bind to microcystin sepharose. This suggests that sds22 may block the microcystin binding site in PP1{gamma}2. A proportion of PP1{gamma}2 in sperm extracts, which is presumably not complexed to sds22, is catalytically active. Fluorescence immunocytochemistry was used to determine the intrasperm localization of PP1{gamma}2 and sds22. Both proteins are present in the tail. They are also present in distinct locations in the head. Our data suggest that PP1{gamma}2 binding to sds22 inhibits its catalytic activity. Mechanisms regulating sds22 binding to PP1{gamma}2 are likely to be important in understanding the biochemical basis underlying development and regulation of sperm function.

1 Supported by NIH grant R01 HD38520.

2 Correspondence. FAX: 330 672 3713; svijayar{at}kent.edu






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