Biliprotein chromophore attachment: chaperone-like function of the PecE subunit of alpha-phycoerythrocyanin lyase.
Biliproteins are post-translationally modified by chromophore addition. In phycoerythrocyanin, the heterodimeric lyase PecE/F covalently attaches phycocyanobilin (PCB) to cysteine-alpha84 of the apoprotein PecA, with concomitant isomerization to phycoviolobilin. We found that: (a) PecA adds autocatalytically PCB, yielding a low absorbance, low fluorescence PCB.PecA adduct, termed P645 according to its absorption maximum; (b) In the presence of PecE, a high absorbance, high fluorescence PCB.PecA adduct is formed, termed P641; (c) PecE is capable of transforming P645 to P641; (d) When in stop-flow experiments, PecA and PecE were preincubated before chromophore addition, a red-shifted intermediate (P650, tau=32 ms) was observed followed by a second, which was blue-shifted (P605, tau=0.5 s), and finally a third (P638, tau=14 s) that yielded the adduct (P641, tau=20 min); (e) The reaction was slower, and P605 was missing, if PecA and PecE were not preincubated; (f) Gel filtration gave no evidence of a stable complex between PecA and PecE; however, complex formation is induced by adding PCB; and (g) A red-shifted intermediate was also formed, but more slowly, with phycoerythrobilin, and denaturation showed that this is not yet covalently bound. We conclude, therefore, that PecA and PecE form a weak complex that is stabilized by PCB, that the first reaction step involves a conformational change and/or protonation of PCB, and that PecE has a chaperone-like function on the chromoprotein.
Böhm
Stephan
S
Department Biologie I, Bereich Botanik, Universität München, München D-80638, Germany.
Endres
Stefanie
S
Scheer
Hugo
H
Zhao
Kai-Hong
KH
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D000458:Cyanobacteria / Q000737:chemistry* / Q000378:metabolism; D005453:Fluorescence; D008190:Lyases / Q000737:chemistry* / Q000378:metabolism; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism; D052980:Phycobilins / Q000737:chemistry* / Q000378:metabolism; D010798:Phycocyanin / Q000737:chemistry* / Q000378:metabolism; D011489:Protein Denaturation; D011499:Protein Processing, Post-Translational / Q000502:physiology
D001426:Bacterial Proteins; D018832:Molecular Chaperones; D046912:Multiprotein Complexes; D052980:Phycobilins; C038397:phycoerythrocyanin; D010798:Phycocyanin; C011069:phycocyanobilin; D008190:Lyases; C093743:phycoerythrocyanin alpha-subunit phycobiliviolin lyase protein, bacteria