title: Structural basis for cpSRP43 chromodomain selectivity and dynamics in Alb3 insertase interaction.
abstract: Canonical membrane protein biogenesis requires co-translational delivery of ribosome-associated proteins to the Sec translocase and depends on the signal recognition particle (SRP) and its receptor (SR). In contrast, high-throughput delivery of abundant light-harvesting chlorophyll a,b-binding proteins (LHCPs) in chloroplasts to the Alb3 insertase occurs post-translationally via a soluble transit complex including the cpSRP43/cpSRP54 heterodimer (cpSRP). Here we describe the molecular mechanisms of tethering cpSRP to the Alb3 insertase by specific interaction of cpSRP43 chromodomain 3 with a linear motif in the Alb3 C-terminal tail. Combining NMR spectroscopy, X-ray crystallography and biochemical analyses, we dissect the structural basis for selectivity of chromodomains 2 and 3 for their respective ligands cpSRP54 and Alb3, respectively. Negative cooperativity in ligand binding can be explained by dynamics in the chromodomain interface. Our study provides a model for membrane recruitment of the transit complex and may serve as a prototype for a functional gain by the tandem arrangement of chromodomains.
authors.affiliation: Heidelberg University Biochemistry Center (BZH), INF 328, Heidelberg D-69120, Germany.
authors.forename: Annemarie
authors.initials: A
authors.lastname: Horn
authors.affiliation: Center for Integrated Protein Science Munich at Biomolecular NMR Spectroscopy, Department Chemie, Technische Universität München, Lichtenbergstrasse 4, Garching DE-85747, Germany.|Institute of Structural Biology, Helmholtz Center Munich, Ingolstädter Landstrasse 1, Neuherberg D-85764, Germany.
authors.forename: Janosch
authors.initials: J
authors.lastname: Hennig
authors.affiliation: Heidelberg University Biochemistry Center (BZH), INF 328, Heidelberg D-69120, Germany.
authors.forename: Yasar L
authors.identifier: http://orcid.org/0000-0002-4364-1372
authors.initials: YL
authors.lastname: Ahmed
authors.affiliation: Heidelberg University Biochemistry Center (BZH), INF 328, Heidelberg D-69120, Germany.
authors.forename: Gunter
authors.initials: G
authors.lastname: Stier
authors.affiliation: Heidelberg University Biochemistry Center (BZH), INF 328, Heidelberg D-69120, Germany.
authors.forename: Klemens
authors.initials: K
authors.lastname: Wild
authors.affiliation: Center for Integrated Protein Science Munich at Biomolecular NMR Spectroscopy, Department Chemie, Technische Universität München, Lichtenbergstrasse 4, Garching DE-85747, Germany.|Institute of Structural Biology, Helmholtz Center Munich, Ingolstädter Landstrasse 1, Neuherberg D-85764, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Sattler
authors.affiliation: Heidelberg University Biochemistry Center (BZH), INF 328, Heidelberg D-69120, Germany.
authors.forename: Irmgard
authors.initials: I
authors.lastname: Sinning
mesh_terms: D020816:Amino Acid Motifs; D017360:Arabidopsis; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D061146:Chlorophyll Binding Proteins; D003460:Crystallization; D018360:Crystallography, X-Ray; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes; D019906:Nuclear Magnetic Resonance, Biomolecular; D053838:Scattering, Small Angle; D018271:Signal Recognition Particle / Q000737:chemistry / Q000378:metabolism*
chemical_list: C106404:ALBINO 3 protein, Arabidopsis; D029681:Arabidopsis Proteins; D061146:Chlorophyll Binding Proteins; D045342:Light-Harvesting Protein Complexes; C091479:SRP54A protein, Arabidopsis; D018271:Signal Recognition Particle; C091480:Srp54-2 protein, Arabidopsis; C091481:Srp54-3 protein, Arabidopsis; C568473:cpSRP43 protein, Arabidopsis; D019204:GTP-Binding Proteins