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  • Title: 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.
    Author: Reinbothe C, Lepinat A, Deckers M, Beck E, Reinbothe S.
    Journal: J Biol Chem; 2003 Jan 10; 278(2):816-22. PubMed ID: 12401791.
    Abstract:
    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.
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