A pentapeptide motif related to a pigment binding site in the major light-harvesting protein of photosystem II, LHCII, governs substrate-dependent plastid import of NADPH:protochlorophyllide oxidoreductase A.
NADPH:protochlorophyllide (Pchlide) oxidoreductase (POR) A is the only known example thus far of a nucleus-encoded plastid protein that is imported to its final destination in a substrate-dependent, Pchlide-regulated manner. Previous work has shown that the cytosolic PORA precursor (pPORA) does not utilize the general import site but uses a distinct translocon designated the Pchlide-dependent translocon complex. Here we demonstrate that a pentapeptide motif, threonine-threonine-serine-proline-glycine (TTSPG) in pPORA's transit peptide (transA), is involved in Pchlide-dependent transport. Deletion of this motif from the COOH-terminal end of transA abolished both Pchlide binding and protein import. Incorporation of the TTSPG motif into normally non-Pchlide-responsive transit sequences conferred the pigment binding properties onto the engineered chimeric precursors but was insufficient to render protein import substrate dependent. An additional motif was identified in the NH(2)-terminal part of transA that was needed for binding of the precursor to the Pchlide-dependent translocon complex. Point mutations of the TTSPG motif identified glycine as the Pchlide binding site. By analogy to the major light-harvesting chlorophyll a/b binding protein of photosystem II, we propose that the peptidyl carbonyl oxygen of glycine may bind directly or via a water molecule to the central Mg atom of the pigment.
Reinbothe
Christiane
C
Universität Bayreuth, Lehrstuhl für Pflanzenphysiologie, Bayreuth, Germany. christiane.reinbothe@uni-beyreuth.de
Pollmann
Stephan
S
Phetsarath-Faure
Phetaphine
P
Quigley
Françoise
F
Weisbeek
Peter
P
Reinbothe
Steffen
S
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D002736:Chloroplasts / Q000378:metabolism*; D017353:Gene Deletion; D001467:Hordeum / Q000235:genetics / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D010860:Pigments, Biological / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D021381:Protein Transport; D016415:Sequence Alignment
D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase; D011494:Protein Kinases; C120337:light-harvesting complex II kinase