A linking function for the cellulose-binding protein SP85 in the spore coat of Dictyostelium discoideum.

Journal Article (Journal Article)

SP85 is a multidomain protein of the Dictyostelium spore coat whose C-terminal region binds cellulose in vitro. To map domains critical for localizing SP85 and for binding to other proteins in vivo, its N- and C-terminal regions, and a hybrid fusion of the N- and C-regions, were expressed in prespore cells. Immunofluorescence showed that only the N-terminal region and the N/C-hybrid accumulated in prespore vesicles, where coat proteins are normally stored prior to secretion. In contrast, only the C-terminal region and N/C-hybrid were incorporated into the coat after secretion. To determine if SP85 is important for the incorporation of other coat proteins, an SP85-null strain was created and found to mislocalize the coat protein SP65 to the interspore matrix. In vitro binding studies demonstrated that the SP85 C-terminal region bound SP65 and cellulose simultaneously, and SP65 incorporation was rescued in vivo by the C-terminal region. SP85-null spores showed increased latent permeability to a fluorescent lectin probe and accelerated germination times, and decreased buoyant density of their coats, suggesting that coat barrier functions were compromised. Dominant negative reductions in barrier functions also resulted from expression of the SP85 terminal regions, suggesting that a linking activity was important for SP85's function. Thus, separate domains of SP85 specify prespore vesicle compartmentalization and coat incorporation, and additional domains link SP65 to the coat and simultaneously interact with other binding partners which contribute to coat barrier functions.

Full Text

Duke Authors

Cited Authors

  • Zhang, Y; Zhang, P; West, CM

Published Date

  • December 1999

Published In

Volume / Issue

  • 112 ( Pt 23) /

Start / End Page

  • 4367 - 4377

PubMed ID

  • 10564654

International Standard Serial Number (ISSN)

  • 0021-9533

Digital Object Identifier (DOI)

  • 10.1242/jcs.112.23.4367


  • eng

Conference Location

  • England