The Acidic Domains of the Toc159 Chloroplast Preprotein Receptor Family are Instrinsically Disordered Protein Domains

Background: 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. Results: 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. Conclusions: 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

The acidic domains of the Toc159 chloroplast preprotein receptor family are intrinsically disordered protein domains

<p>Abstract</p> <p>Background</p> <p>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.</p> <p>Results</p> <p>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 <it>Arabidopsis </it>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.</p> <p>Conclusions</p> <p>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.</p

Trans-Bilayer Ion Conduction by Proline Containing Cyclic Hexapeptides and Effects of Amino Acid Substitutions on Ion Conducting Properties

Several ion channel forming cyclic peptides have been reported over the past two decades and various ion conducting mechanisms have been proposed. In this article, we report on amino acid substitutions in cyclic hexapeptides and their effects on the ion conducting properties of these peptides. Cyclic hexapeptides, cyclo(Pro-Xxx-Yyy)2, containing two Pro residues, were used as the main framework. The substitution is performed at the Xxx positions with cationic/hydrophilic Lys or hydrophobic Leu. Yyy positions were substituted with D-Phe, D-Ala, or Gly. The peptides which were absent Lys residues showed ion conducting profiles with clear transitions of electric currents, whereas the peptides containing Lys residues tended to exhibit spiky or burst-like profiles. These profiles were altered single state profiles by the protection of ε-amino groups with aromatic protecting groups. The protected analogs exhibited significant decrease in ion conductance. These results indicated that peptides containing Lys conduct ions without forming ring stacked tube-like structure. Ion channel properties were also affected by conformational changes of the cyclic peptides induced by substitution of the Yyy positions. Enhancement of intramolecular β-turn structures of cyclic peptides tended to decrease their ion conductance values

Membrane Proteins: Structure, Function and Motion

Cell membranes are intricate multicomponent supramolecular structures, with a complex variable morphology and chemical composition [...

Uncoupling Proteins and Regulated Proton Leak in Mitochondria

Higher concentration of protons in the mitochondrial intermembrane space compared to the matrix results in an electrochemical potential causing the back flux of protons to the matrix. This proton transport can take place through ATP synthase complex (leading to formation of ATP) or can occur via proton transporters of the mitochondrial carrier superfamily and/or membrane lipids. Some mitochondrial proton transporters, such as uncoupling proteins (UCPs), transport protons as their general regulating function; while others are symporters or antiporters, which use the proton gradient as a driving force to co-transport other substrates across the mitochondrial inner membrane (such as phosphate carrier, a symporter; or aspartate/glutamate transporter, an antiporter). Passage (or leakage) of protons across the inner membrane to matrix from any route other than ATP synthase negatively impacts ATP synthesis. The focus of this review is on regulated proton transport by UCPs. Recent findings on the structure and function of UCPs, and the related research methodologies, are also critically reviewed. Due to structural similarity of members of the mitochondrial carrier superfamily, several of the known structural features are potentially expandable to all members. Overall, this report provides a brief, yet comprehensive, overview of the current knowledge in the field

The Acidic Domains of the Toc159 Chloroplast Preprotein Receptor Family are Instrinsically Disordered Protein Domains

Background: 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. Results: 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. Conclusions: 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