Purification of ferredoxin-NADP+ oxidoreductase from thermophilic cyanobacterium Synechococcus elongatus.

Abstract

Ferredoxin-NADP+ oxidoreductase (FNR) of cyanobacteria is composed of three domains unlike higher plant FNRs. The N-terminal domain, ranging ca. 9 kDa, is homologous to CpcD phycobilisome linker polypeptide (1). It is suggested from these facts that cyanobacterial FNR is likely docked at phycobilisome rod by CpcD-like domain (1). However, FNR proteins purified from cyanobacteria so far showed the molecular mass of ca. 31.5-36 kDa without CpcD-like domain. We tried purification of FNR from thermophilic cyanobacterium, S. elongatus. The FNR showed a single peak (78 kDa) on Superose 12 gel filtration chromatography, but 45 kDa FNR band and two phycobiliproteins bands on SDS-PAGE, indicating that S. elongatus FNR bound with phycobiliproteins, probably phycocyanin monomer, even after dissociation of phycobilisome. FNR was successfully separated from phycobiliproteins by hydroxyapatite chromatography. However, 45kDa FNR released from phycobiliprotein, was easily attacked by intrinsic protease(s) at the specific cleavage site. These results on cyanobacterial FNR should give us the important information of FNR localization on thylakoid membrane and of electron transfer mechanism around PS I. We describe the state of FNR molecule from thermophilic cyanobacterium S. elongatus, in addition to the biochemical properties. (1) Schluchter, W. M. and Bryant, D. A. (1992) Biochemistry 31, 3092-3102.