TY - JOUR
T1 - Small Cab-like proteins regulating tetrapyrrole biosynthesis in the cyanobacterium Synechocystis sp. Pcc 6803
AU - Xu, Hong
AU - Vavilin, Dmitrii
AU - Funk, Christiane
AU - Vermaas, Willem
N1 - Funding Information:
This work was supported by a grant from the US Department of Energy (DE-FG03-95ER20180).
PY - 2002
Y1 - 2002
N2 - In the cyanobacterium Synechocystis sp. PCC 6803 five open reading frames (scpA-scpE) have been identified that code for single-helix proteins resembling helices I and III of chlorophyll a/b-binding (Cab) antenna proteins from higher plants. They have been named SCPs (small Cab-like proteins). Deletion of a single scp gene in a wild-type or in a photosystem I-less (PS I-less) strain has little effect. However, the effects of functional deletion of scpB or scpE were remarkable under conditions where chlorophyll availability was limited. When cells of a strain lacking PS I and chlL (coding for a polypeptide needed for light-independent protochlorophyllide reduction) were grown in darkness, the phycobilin and protochlorophyllide levels decreased upon deletion of scpB or scpE and the protoheme level was reduced in the strain lacking scpE. Addition of δ-aminolevulinic acid (ALA) in darkness drastically increased the level of Mg-protoporphyrin IX and Mg-protoporphyrin 1X monomethyl ester in the PS 1-less/chlL-/scpE- strain, whereas PChlide accumulated in the PS I-less/chIL-/scpB- strain. In the PS I-less/chlL- control strain ALA supplementation did not lead to large changes in the levels of tetrapyrrole biosynthesis intermediates. We propose that ScpE and ScpB regulate tetrapyrrole biosynthesis as a function of pigment availability. This regulation occurs primarily at an early step of tetrapyrrole biosynthesis, prior to ALA. In view of the conserved nature of chlorophyll-binding sites in these proteins, it seems likely that regulation by SCPs occurs as a function of chlorophyll availability, with SCPs activating chlorophyll biosynthesis steps when they do not have pigments bound.
AB - In the cyanobacterium Synechocystis sp. PCC 6803 five open reading frames (scpA-scpE) have been identified that code for single-helix proteins resembling helices I and III of chlorophyll a/b-binding (Cab) antenna proteins from higher plants. They have been named SCPs (small Cab-like proteins). Deletion of a single scp gene in a wild-type or in a photosystem I-less (PS I-less) strain has little effect. However, the effects of functional deletion of scpB or scpE were remarkable under conditions where chlorophyll availability was limited. When cells of a strain lacking PS I and chlL (coding for a polypeptide needed for light-independent protochlorophyllide reduction) were grown in darkness, the phycobilin and protochlorophyllide levels decreased upon deletion of scpB or scpE and the protoheme level was reduced in the strain lacking scpE. Addition of δ-aminolevulinic acid (ALA) in darkness drastically increased the level of Mg-protoporphyrin IX and Mg-protoporphyrin 1X monomethyl ester in the PS 1-less/chlL-/scpE- strain, whereas PChlide accumulated in the PS I-less/chIL-/scpB- strain. In the PS I-less/chlL- control strain ALA supplementation did not lead to large changes in the levels of tetrapyrrole biosynthesis intermediates. We propose that ScpE and ScpB regulate tetrapyrrole biosynthesis as a function of pigment availability. This regulation occurs primarily at an early step of tetrapyrrole biosynthesis, prior to ALA. In view of the conserved nature of chlorophyll-binding sites in these proteins, it seems likely that regulation by SCPs occurs as a function of chlorophyll availability, with SCPs activating chlorophyll biosynthesis steps when they do not have pigments bound.
KW - Chlorophyll biosynthesis
KW - Cyanobacteria
KW - Feedback regulation
KW - Small Cab-like proteins
KW - Tetrapyrrole biosynthesis pathway
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U2 - 10.1023/A:1014900806905
DO - 10.1023/A:1014900806905
M3 - Article
C2 - 11999371
AN - SCOPUS:0036010856
SN - 0167-4412
VL - 49
SP - 149
EP - 160
JO - Plant Molecular Biology
JF - Plant Molecular Biology
IS - 2
ER -