Chromophore attachment to biliproteins: specificity of PecE/PecF, a lyase-isomerase for the photoactive 3(1)-cys-alpha 84-phycoviolobilin chromophore of phycoerythrocyanin.
PecE and PecF, the products of two phycoerythrocyanin lyase genes (pecE and pecF) of Mastigocladus laminosus (Fischerella), catalyze two reactions: (1) the regiospecific addition of phycocyanobilin (PCB) to Cys-alpha 84 of the phycoerythrocyanin alpha-subunit (PecA), and (2) the Delta 4-->Delta 2 isomerization of the PCB to the phycoviolobilin (PVB)-chromophore [Zhao et al. (2000) FEBS Lett. 469, 9-13]. The alpha-apoprotein (PecA) as well PecE and PecF were overexpressed from two strains of M. laminosus, with and without His-tags. The products of the spontaneous addition of PCB to PecA, and that of the reaction catalyzed by PecE/F, were characterized by their photochemistry and by absorption, fluorescence, circular dichroism of the four states obtained by irradiation with light (15-Z/E isomers of the chromophore) and/or modification of Cys-alpha 98/99 with thiol-directed reagents. The spontaneous addition leads to a 3(1)-Cys-PCB adduct, which is characteristic of allophycocyanins and phycocyanins, while the addition catalyzed by PecE and PecF leads to a 3(1)-Cys-PVB adduct which after purification was identical to alpha-PEC. The specificity and kinetics of the chromophore additions were investigated with respect to the structure of the bilin substrate: The 3-ethylidene-bilins, viz., PCB, its 18-vinyl analogue phytochromobilin, phycoerythrobilin and its dimethylester, react spontaneously to yield the conventional addition products (3-H, 3(1)-Cys), while the 3-vinyl-substituted bilins, viz., bilirubin and biliverdin, were inactive. Only phycocyanobilin and phytochromobilin are substrates to the addition-isomerization reaction catalyzed by PecE/F. The slow spontaneous addition of phycoerythrobilin is not influenced, and there is in particular no catalyzed isomerization to urobilin.
Storf
M
M
Botanisches Institut, Universität München, Germany.
Parbel
A
A
Meyer
M
M
Strohmann
B
B
Scheer
H
H
Deng
M G
MG
Zheng
M
M
Zhou
M
M
Zhao
K H
KH
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D000458:Cyanobacteria / Q000201:enzymology / Q000235:genetics; D008190:Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015394:Molecular Structure; D010777:Photochemistry; D052980:Phycobilins; D010798:Phycocyanin / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
D001426:Bacterial Proteins; D052980:Phycobilins; D011994:Recombinant Proteins; C038397:phycoerythrocyanin; D010798:Phycocyanin; D008190:Lyases; C093743:phycoerythrocyanin alpha-subunit phycobiliviolin lyase protein, bacteria