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-α84 of the phycoerythrocyanin α-subunit (PecA), and (2) the Δ4→Δ2 isomerization of the PCB to the phycoviolobilin (PVB)-chromophore [Zhao et al. (2000) FEBS Lett. 469, 9−13]. The α-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-α98/99 with thiol-directed reagents. The spontaneous addition leads to a 31-Cys-PCB adduct, which is characteristic of allophycocyanins and phycocyanins, while the addition catalyzed by PecE a...