Characterization of S-AKAP84, a Novel Developmentally Regulated A Kinase Anchor Protein of Male Germ Cells

doi:10.1074/jbc.270.46.27804

Characterization of S-AKAP84, a Novel Developmentally Regulated A Kinase Anchor Protein of Male Germ Cells (*)

From the (1) Department of Molecular Pharmacology, Atran Laboratories, Albert Einstein College of Medicine, Bronx, New York, 10461 and the
(2) Department of Obstetrics and Gynecology, Division of Reproductive Biology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104

Abstract

In mammalian spermatozoa, most of the type IIα isoform of cAMP-dependent protein kinase (PKAIIα) is anchored at the cytoplasmic surface of a specialized array of mitochondria in the flagellar cytoskeleton. This places the catalytic subunits of PKAIIα in proximity with potential target substrates in the cytoskeleton. The mechanism by which PKAIIα is anchored at the outer surface of germ cell mitochondria has not been elucidated. We now report the cloning of a cDNA that encodes a novel, germ cell A kinase anchor protein (AKAP) designated S-AKAP84. S-AKAP84 comprises 593 amino acids and contains a centrally located domain that avidly binds regulatory subunits (RIIα and RIIβ) of PKAIIα and PKAIIβ. The 3.2-kilobase S-AKAP84 mRNA and the cognate S-AKAP84 RII binding protein are expressed principally in the male germ cell lineage. Expression of S-AKAP84 is tightly regulated during development. The protein accumulates as spermatids undergo nuclear condensation and tail elongation. The timing of S-AKAP84 expression is correlated with the de novo accumulation of RIIα and RIIβ subunits and the migration of mitochondria from the cytoplasm (round spermatids) to the cytoskeleton (midpiece in elongating spermatids). Residues 1-30 at the NH terminus of S-AKAP84 constitute a putative signal/anchor sequence that may target the protein to the outer mitochondrial membrane. Immunofluorescence analysis demonstrated that S-AKAP84 is co-localized with mitochondria in the flagellum.

Footnotes

↵* This work was supported in part by National Institutes of Health Grant GM22792 (to C. S. R.) and U.S. Department of Agriculture Grant 92-37205-8050 (to S. B. M.) The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) U34074[GenBank].
↵¹ The abbreviations used are:

PKA

protein kinase A (cAMP-dependent protein kinase)

R

regulatory subunit of cAMP-dependent protein kinase

C

catalytic subunit of cAMP-dependent protein kinase

AKAP

protein kinase A anchor protein

kb

kilobase(s).
↵² R. Y. Lin and C. S. Rubin, unpublished observations.
↵³ Q. Chen, R. Y. Lin, and C. S. Rubin, unpublished observations.
↵⁴ The fibrous sheath AKAP designated p82 (17) is not bound by anti-S-AKAP84 IgGs, and its binding activity is not detected under the overlay assay conditions used in the present studies.
- Received June 14, 1995.
- Revision received August 16, 1995.