Structural insights into membrane targeting by the flagellar calcium-binding protein (FCaBP), a myristoylated and palmitoylated calcium sensor in Trypanosoma cruzi

Jennifer N. Wingard, Jane Ladner, Murugendra Vanarotti, Andrew J Fisher, Howard Robinson, Kathryn T. Buchanan, David M. Engman, James B. Ames

Research output: Contribution to journalArticle

23 Scopus citations

Abstract

The flagellar calcium-binding protein (FCaBP) of the protozoan Trypanosoma cruzi is targeted to the flagellar membrane where it regulates flagellar function and assembly. As a first step toward understanding the Ca 2+-induced conformational changes important for membrane-targeting, we report here the x-ray crystal structure of FCaBP in the Ca2+-free state determined at 2.2 Å resolution. The first 17 residues from the N terminus appear unstructured and solvent-exposed. Residues implicated in membrane targeting (Lys-19, Lys-22, and Lys-25) are flanked by an exposed N-terminal helix (residues 26-37), forming a patch of positive charge on the protein surface that may interact electrostatically with flagellar membrane targets. The four EF-hands in FCaBP each adopt a "closed conformation" similar to that seen in Ca2+-free calmodulin. The overall fold of FCaBP is closest to that of grancalcin and other members of the penta EF-hand superfamily. Unlike the dimeric penta EF-hand proteins, FCaBP lacks a fifth EF-hand and is monomeric. The unstructured N-terminal region of FCaBP suggests that its covalently attached myristoyl group at the N terminus may be solvent-exposed, in contrast to the highly sequestered myristoyl group seen in recoverin and GCAP1. NMR analysis demonstrates that the myristoyl group attached to FCaBP is indeed solvent-exposed in both the Ca2+-free and Ca 2+-bound states, and myristoylation has no effect on protein structure and folding stability. We propose that exposed acyl groups at the N terminus may anchor FCaBP to the flagellar membrane and that Ca 2+-induced conformational changes may control its binding to membrane-bound protein targets.

Original languageEnglish (US)
Pages (from-to)23388-23396
Number of pages9
JournalJournal of Biological Chemistry
Volume283
Issue number34
DOIs
StatePublished - Aug 22 2008

ASJC Scopus subject areas

  • Biochemistry
  • Cell Biology
  • Molecular Biology

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