title: Evolutionarily evolved discriminators in the 3-TPR domain of the Toc64 family involved in protein translocation at the outer membrane of chloroplasts and mitochondria.
abstract: Transport of polypeptides across membranes is a general and essential cellular process utilised by molecular machines. At least one component of these complexes contains a domain composed of three tetratricopeptide repeat (3-TPR) motifs. We have focussed on the receptor Toc64 to elucidate the evolved functional specifications of its 3-TPR domain. Toc64 is a component of the Toc core complex and functionally replaces Tom70 at the outer membrane of mitochondria in plants. Its 3-TPR domain recognises the conserved C-terminus of precursor-bound chaperones. We built homology models of the 3-TPR domain of chloroplastic Toc64 from different species and of the mitochondrial isoform from Arabidopsis. Guided by modelling, we identified residues essential for functional discrimination of the differently located isoforms to be located almost exclusively on the convex surface of the 3-TPR domain. The only exception is at568Ser/ps557Met, which is positioned in the ligand-binding groove. The functional implications of the homology models are discussed.
authors.affiliation: Cluster of Excellence and Center of Membrane Proteomics, Institute for Molecular Biosciences, Johann Wolfgang Goethe University, Max-von-Laue-Str. 9, N200, 60438, Frankfurt am Main, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Mirus
authors.forename: Tihana
authors.initials: T
authors.lastname: Bionda
authors.forename: Arndt
authors.initials: A
authors.lastname: von Haeseler
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D002736:Chloroplasts / Q000378:metabolism*; D003198:Computer Simulation; D019143:Evolution, Molecular; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D025341:Principal Component Analysis; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport
chemical_list: D029681:Arabidopsis Proteins; D018841:HSP90 Heat-Shock Proteins; D008565:Membrane Proteins; C488374:Toc64 protein, Arabidopsis