The acidic domains of the Toc159 chloroplast preprotein receptor family are intrinsically disordered protein domains
1 Department of Biology, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada
2 Department of Biology, University of Waterloo, Waterloo, ON, N2L 3G1, Canada
3 Department of Chemistry, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada
4 Current address: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
BMC Biochemistry 2009, 10:35 doi:10.1186/1471-2091-10-35Published: 30 December 2009
The Toc159 family of proteins serve as receptors for chloroplast-destined preproteins. They directly bind to transit peptides, and exhibit preprotein substrate selectivity conferred by an unknown mechanism. The Toc159 receptors each include three domains: C-terminal membrane, central GTPase, and N-terminal acidic (A-) domains. Although the function(s) of the A-domain remains largely unknown, the amino acid sequences are most variable within these domains, suggesting they may contribute to the functional specificity of the receptors.
The physicochemical properties of the A-domains are characteristic of intrinsically disordered proteins (IDPs). Using CD spectroscopy we show that the A-domains of two Arabidopsis Toc159 family members (atToc132 and atToc159) are disordered at physiological pH and temperature and undergo conformational changes at temperature and pH extremes that are characteristic of IDPs.
Identification of the A-domains as IDPs will be important for determining their precise function(s), and suggests a role in protein-protein interactions, which may explain how these proteins serve as receptors for such a wide variety of preprotein substrates.