Browsing by Author "Golbeck, John H."

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Reaction centers of the thermophilic microaerophile, Chloracidobacterium thermophilum (Acidobacteria) I: biochemical and biophysical characterization
(Springer Science and Business Media LLC, 2019-06) He, Zhihui; Ferlez, Bryan; Kurashov, Vasily; Tank, Marcus; Golbeck, John H.; Bryant, Donald A.
Chloracidobacterium thermophilum is a microaerophilic, anoxygenic member of the green chlorophototrophic bacteria. This bacterium is the first characterized oxygen-requiring chlorophototroph with chlorosomes, the FMO protein, and homodimeric type-1 reaction centers (RCs). The RCs of C. thermophilum are also unique because they contain three types of chlorophylls, bacteriochlorophyll aP esterified with phytol, Chl aPD esterified with D2,6- phytadienol, and Zn-BChl aP¢ esterified with phytol, in the approximate molar ratio 32:24:4. The light-induced difference spectrum of these RCs had a bleaching maximum at 839 nm and also revealed an electrochromic bandshift that is probably derived from a BChl a molecule near P840+. The FX [4Fe-4S] cluster had a midpoint potential of ca. –581 mV, and the spectroscopic properties of the P+ FX– spin-polarized radical-pair were very similar to those of reaction centers of heliobacteria and green sulfur bacteria. The data further indicate that electron transfer occurs directly from A0– to FX, as occurs in other homodimeric Type-1 RCs. Washing experiments with isolated membranes suggested that the PscB subunit of these reaction centers is more tightly bound than PshB in heliobacteria. Thus, the reaction centers of C. thermophilum have some properties that resemble other homodimeric reaction centers but also have specific properties that are more similar to those of Photosystem I. These differences probably contribute to protection of the electron transfer chain from oxygen, contributing to the oxygen tolerance of this microaerophile.
The structure of Photosystem I acclimated to far-red light illuminates an ecologically important acclimation process in photosynthesis
(2020-02) Gisriel, Christopher; Shen, Gaozhong; Kurashov, Vasily; Ho, Ming-Yang; Zhang, Shangji; Williams, Dewight; Golbeck, John H.; Fromme, Petra; Bryant, Donald A.
Phototrophic organisms are superbly adapted to different light environments but often must acclimate to challenging competition for visible light wavelengths in their niches. Some cyanobacteria overcome this challenge by expressing paralogous photosynthetic proteins and by synthesizing and incorporating ~8% chlorophyll f into their Photosystem I (PSI) complexes, enabling them to grow under far-red light (FRL). We solved the structure of FRL-acclimated PSI from the cyanobacterium Fischerella thermalis PCC 7521 by single-particle, cryo–electron microscopy to understand its structural and functional differences. Four binding sites occupied by chlorophyll f are proposed. Subtle structural changes enable FRL-adapted PSI to extend light utilization for oxygenic photosynthesis to nearly 800 nm. This structure provides a platform for understanding FRL-driven photosynthesis and illustrates the robustness of adaptive and acclimation mechanisms in nature.