TY - JOUR
T1 - Isolation and characterization of homodimeric type-I reaction center complex from Candidatus chloracidobacterium thermophilum, an aerobic chlorophototroph
AU - Tsukatani, Yusuke
AU - Romberger, Steven P.
AU - Golbeck, John H.
AU - Bryant, Donald A.
PY - 2012/2/17
Y1 - 2012/2/17
N2 - The recently discovered thermophilic acidobacterium Candidatus Chloracidobacterium thermophilum is the first aerobic chlorophototroph that has a type-I, homodimeric reaction center (RC). This organism and its type-I RCs were initially detected by the occurrence of pscA gene sequences, which encode the core subunit of the RC complex, in metagenomic sequence data derived from hot spring microbial mats. Here, we report the isolation and initial biochemical characterization of the type-I RC from Ca. C. thermophilum. After removal of chlorosomes, crude membranes were solubilized with 0.1% (w/v) n-dodecyl β-D-maltoside, and the RC complex was purified by ion-exchange chromatography. The RC complex comprised only two polypeptides: the reaction center core protein PscA and a 22-kDa carotenoid-binding protein denoted CbpC. The absorption spectrum showed a large, broad absorbance band centered at ∼483 nm from carotenoids as well as smaller Qy absorption bands at 672 and 812 nm from chlorophyll a and bacteriochlorophyll a, respectively. The light-induced difference spectra of whole cells, membranes, and the isolated RC showed maximal bleaching at 840 nm, which is attributed to the special pair and which we denote as P840. Making it unique among homodimeric type-I RCs, the isolated RC was photoactive in the presence of oxygen. Analyses by optical spectroscopy, chromatography, and mass spectrometry revealed that the RC complex contained 10.3 bacteriochlorophyll aP, 6.4 chlorophyll a PD, and 1.6 Zn-bacteriochlorophyll aP′ molecules per P840 (12.8:8.0: 2.0). The possible functions of the Zn-bacteriochlorophyll aP′molecules and the carotenoid-binding protein are discussed.
AB - The recently discovered thermophilic acidobacterium Candidatus Chloracidobacterium thermophilum is the first aerobic chlorophototroph that has a type-I, homodimeric reaction center (RC). This organism and its type-I RCs were initially detected by the occurrence of pscA gene sequences, which encode the core subunit of the RC complex, in metagenomic sequence data derived from hot spring microbial mats. Here, we report the isolation and initial biochemical characterization of the type-I RC from Ca. C. thermophilum. After removal of chlorosomes, crude membranes were solubilized with 0.1% (w/v) n-dodecyl β-D-maltoside, and the RC complex was purified by ion-exchange chromatography. The RC complex comprised only two polypeptides: the reaction center core protein PscA and a 22-kDa carotenoid-binding protein denoted CbpC. The absorption spectrum showed a large, broad absorbance band centered at ∼483 nm from carotenoids as well as smaller Qy absorption bands at 672 and 812 nm from chlorophyll a and bacteriochlorophyll a, respectively. The light-induced difference spectra of whole cells, membranes, and the isolated RC showed maximal bleaching at 840 nm, which is attributed to the special pair and which we denote as P840. Making it unique among homodimeric type-I RCs, the isolated RC was photoactive in the presence of oxygen. Analyses by optical spectroscopy, chromatography, and mass spectrometry revealed that the RC complex contained 10.3 bacteriochlorophyll aP, 6.4 chlorophyll a PD, and 1.6 Zn-bacteriochlorophyll aP′ molecules per P840 (12.8:8.0: 2.0). The possible functions of the Zn-bacteriochlorophyll aP′molecules and the carotenoid-binding protein are discussed.
UR - http://www.scopus.com/inward/record.url?scp=84857272963&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84857272963&partnerID=8YFLogxK
U2 - 10.1074/jbc.M111.323329
DO - 10.1074/jbc.M111.323329
M3 - Article
C2 - 22184116
AN - SCOPUS:84857272963
SN - 0021-9258
VL - 287
SP - 5720
EP - 5732
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 8
ER -