DETECTION AND LOCALIZATION OF SYNEXIN (ANNEXIN-VII) IN XENOPUS ADULT AND EMBRYONIC-TISSUES USING AN ANTIBODY TO THE XENOPUS N-TERMINAL PGQMREPEAT DOMAIN

Synexin (Annexin VII) is a widely distributed member of the annexin ge ne family which forms calcium channels and drives calcium-dependent me mbrane fusion. In Xenopus laevis, different synexins contain two to si x tandem repeats of the tetra amino acid sequence PGQM in the unique N -terminal, with a distribution specific to adult tissues and embryonic stages. Immunogold studies using the PGQM-specific polyclonal antibod y showed that synexin is localized in adult muscle to myosin-rich A-ba nds, Z-bands, and T-tubules, and in other adult tissues to nuclei and mitochondria and other formed elements. In oocytes, synexin was also f ound associated with yolk granules. The PGQM: tandem repeats could rep resent interaction sites for other proteins, and we therefore synthesi zed a synthetic peptide containing the maximum six tandem repeats [NH2 -(PGQM)(6)-Y-COOH] to test this hypothesis. We found that the peptide alone could specifically bind and crosslink to different proteins in a tissue-specific manner. In liver, it bound to a single 35-kDa protein . In muscle, it bound to four proteins (35, 45, 48, and 116 kDa). Ther efore, we conclude that the PGQM domain is accessible to specific anti bodies and that the PGQM repeat is sufficiently ordered to unambiguous ly identify specific binding proteins in different Xenopus tissues. (C ) 1996 Academic Press, Inc.