Genetic and Physical Interaction Studies Reveal Functional Similarities between ALBINO3 and ALBINO4 in Arabidopsis.
ALBINO3 (ALB3) is a well-known component of a thylakoid protein-targeting complex that interacts with the chloroplast signal recognition particle (cpSRP) and the cpSRP receptor, chloroplast filamentous temperature-sensitive Y (cpFtsY). Its protein-inserting function has been established mainly for light-harvesting complex proteins, which first interact with the unique chloroplast cpSRP43 component and then are delivered to the ALB3 integrase by a GTP-dependent cpSRP-cpFtsY interaction. In Arabidopsis (Arabidopsis thaliana), a subsequently discovered ALB3 homolog, ALB4, has been proposed to be involved not in light-harvesting complex protein targeting, but instead in the stabilization of the ATP synthase complex. Here, however, we show that ALB3 and ALB4 share significant functional overlap, and that both proteins are required for the efficient insertion of cytochrome f and potentially other subunits of pigment-bearing protein complexes. Genetic and physical interactions between ALB4 and ALB3, and physical interactions between ALB4 and cpSRP, suggest that the two ALB proteins may engage similar sets of interactors for their specific functions. We propose that ALB4 optimizes the insertion of thylakoid proteins by participating in the ALB3-cpSRP pathway for certain substrates (e.g. cytochrome f and the Rieske protein). Although ALB4 has clearly diverged from ALB3 in relation to the partner-recruiting C-terminal domain, our analysis suggests that one putative cpSRP-binding motif has not been entirely lost.
Department of Biology, University of Leicester, Leicester LE1 7RH, United Kingdom (R.T., M.T., P.J.); andDepartment of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., P.J.).
Raphael
R
Trösch
Department of Biology, University of Leicester, Leicester LE1 7RH, United Kingdom (R.T., M.T., P.J.); andDepartment of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., P.J.).
Mats
M
Töpel
Department of Biology, University of Leicester, Leicester LE1 7RH, United Kingdom (R.T., M.T., P.J.); andDepartment of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., P.J.).
Úrsula
Ú
Flores-Pérez
Department of Biology, University of Leicester, Leicester LE1 7RH, United Kingdom (R.T., M.T., P.J.); andDepartment of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (U.F.-P., P.J.) paul.jarvis@plants.ox.ac.uk.
Paul
P
Jarvis
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D045346:Cytochrome b6f Complex / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D030821:Plants, Genetically Modified; D018271:Signal Recognition Particle / Q000235:genetics / Q000378:metabolism; D020524:Thylakoids / Q000235:genetics
C106404:ALBINO 3 protein, Arabidopsis; C512059:Alb4 protein, Arabidopsis; D029681:Arabidopsis Proteins; D018271:Signal Recognition Particle; D045346:Cytochrome b6f Complex