Presence of a [3Fe–4S] cluster in a PsaC variant as a functional component of the photosystem I electron transfer chain in Synechococcus sp. PCC 7002

• Published in: Photosynthesis research Vol. 136; no. 1; pp. 31 - 48
• Main Authors: Pérez, Adam A., Ferlez, Bryan H., Applegate, Amanda M., Walters, Karim, He, Zhihui, Shen, Gaozhong, Golbeck, John H., Bryant, Donald A.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-04-2018; Springer; Springer Nature B.V
• Subjects: Biochemistry; Biomedical and Life Sciences; Electron transfer; Electron transport; Flavodoxin; Gene deletion; Life Sciences; Original Article; Photosynthesis; Photosystem I; Plant Genetics and Genomics; Plant Physiology; Plant Sciences; Synechococcus; Photosystem I; Electron transfer; PsaC; Photosynthesis; Cyanobacteria; Iron–sulfur cluster
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1007/s11120-017-0437-0

A site-directed C14G mutation was introduced into the stromal PsaC subunit of
Synechococcus
sp. strain PCC 7002 in vivo in order to introduce an exchangeable coordination site into the terminal F
B
[4Fe–4S] cluster of Photosystem I (PSI). Using an engineered PSI-less strain (
psaAB
deletion),
psaC
was deleted and replaced with recombinant versions controlled by a strong promoter, and the
psaAB
deletion was complemented. Modified PSI accumulated at lower levels in this strain and supported slower photoautotrophic growth than wild type. As-isolated PSI complexes containing PsaC
C14G
showed resonances with
g
values of 2.038 and 2.007 characteristic of a [3Fe–4S]
1+
cluster. When the PSI complexes were illuminated at 15 K, these resonances partially disappeared and two new sets of resonances appeared. The majority set had
g
values of 2.05, 1.95, and 1.85, characteristic of F
A
−
, and the minority set had
g
values of 2.11, 1.90, and 1.88 from F
B
′ in the modified site. The
S
 = 1/2 spin state of the latter implied the presence of a thiolate as the terminal ligand. The [3Fe–4S] clusters could be partially reconstituted with iron, producing a larger population of [4Fe–4S] clusters. Rates of flavodoxin reduction were identical in PSI complexes isolated from wild type and the PsaC
C14G
variant strain; this implied equivalent capacity for forward electron transfer in PSI complexes that contained [3Fe–4S] and [4Fe–4S] clusters. The development of this cyanobacterial strain is a first step toward translation of in vitro PSI-based biosolar molecular wire systems in vivo and provides new insights into the formation of Fe/S clusters.