The extra loop distinguishing POR from the structurally related short-chain alcohol dehydrogenases is dispensable for pigment binding but needed for the assembly of light-harvesting POR-protochlorophyllide complex.
We have recently discovered a protochlorophyllide (Pchlide)-based light-harvesting complex involved in chlorophyll a biosynthesis. This complex consists of the two previously identified NADPH:protochlorophyllide oxidoreductases (PORs), PORA and PORB, their natural substrates (Pchlide b and Pchlide a, respectively), plus NADPH. These are all held together in a stoichiometry of five PORA-Pchlide b-NADPH complexes and one PORB-Pchlide a-NADPH complex in the prolamellar body of etioplasts. The assembly of this novel light-harvesting POR-Pchlide complex (LHPP) requires both the proper interaction of the PORA and PORB with their cognate substrates as well as the oligomerization of the resulting POR-pigment-NADPH ternary complexes into the native, lipid-containing structure of the etioplast. In this study, we demonstrate that the conserved extra sequence that distinguishes PORA and PORB from the structurally related short-chain alcohol dehydrogenases, is dispensable for pigment binding but needed for the assembly of LHPP. As shown by in vitro mutagenesis, deleting this extra sequence gave rise to assembly-incompetent but pigment-containing PORA and PORB polypeptides.
Reinbothe
Christiane
C
Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, Universitätsstrasse 30, Germany.christiane.reinbothe@uni-bayreuth.de
Lepinat
Anja
A
Deckers
Markus
M
Beck
Erwin
E
Reinbothe
Steffen
S
D000426:Alcohol Dehydrogenase / Q000737:chemistry*; D000595:Amino Acid Sequence; D001467:Hordeum / Q000737:chemistry*; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010940:Plant Proteins / Q000737:chemistry*; D011521:Protochlorophyllide / Q000378:metabolism*
D010940:Plant Proteins; D011521:Protochlorophyllide; D010088:Oxidoreductases; D000426:Alcohol Dehydrogenase; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase