Efficient Light Harvesting in a Dark, Hot, Acidic Environment: The Structure and Function of PSI-LHCI from Galdieria sulphuraria

Abstract

Photosystem I-light harvesting complex I (PSI-LHCI) was isolated from the thermoacidophilic red alga Galdieria sulphuraria, and its structure, composition, and light-harvesting function were characterized by electron microscopy, mass spectrometry, and ultrafast optical spectroscopy. The results show that Galdieria PSI is a monomer with core features similar to those of PSI from green algae, but with significant differences in shape and size. A comparison with the crystal structure of higher plant (pea) PSI-LHCI indicates that Galdieria PSI binds seven to nine light-harvesting proteins. Results from ultrafast optical spectroscopy show that the functional coupling of the LHCI proteins to the PSI core is tighter than in other eukaryotic PSI-LHCI systems reported thus far. This tight coupling helps Galdieria perform efficient light harvesting under the low-light conditions present in its natural endolithic habitat.

Phycobilisome Mobility and Its Role in the Regulation of Light Harvesting in Red Algae

“…Moreover, such a tight coupling between antennae proteins in extremophilic red algae has already been found between PSI and its light-harvesting antennae (Thangaraj et al, 2011). This suggests that the stronger interaction between lightharvesting proteins in extremophilic red algae seems to be a consequence of their adaptation to high temperatures (above 40°C).…”

Isolation and characterization of CAC antenna proteins and photosystem I supercomplex from the cryptophytic alga Rhodomonas salina

“…As for the number of antenna complexes bound to the PSI in R. salina , present data allow only for a rough estimate. However, it can be noted that a number of previous studies on the systems binding similar amount of pigments, such as largest red‐algal PSI supercomplexes (Thangaraj et al , Haniewicz et al ) and related heterokont systems (Bína et al ) estimated nine LHC proteins. Moreover, the apparent mass of the PSI‐LHC supercomplex of R. salina (approximately 750 kDa) corresponds quite well to the size of the PSI‐Lhca complex, also containing nine antenna subunits, from the green alga Chlamydomonas reinhardti (approximately 770 kDa, Drop et al ).…”

“…Looking at the pigment data (Table ), it is possible to get an estimate of the pigment composition of PSI antenna, built on the assumption that R. salina PSI core , like all known PSI cores, binds approximately 20 carotenes +100 Chl a . For instance, utilizing red‐algal PSI core value of 21 + 97 (Pi et al ) after normalizing to carotene, one gets approximately 230 Chl a per PSI supercomplex, a standard value for PSI supercomplexes from a broad phylogenetic range, from red algae, heterokonts to green algae (Kargul et al , Ikeda et al , Thangaraj et al , Bína et al ). The pigment content of PSI antenna can then be computed by the difference (Table ).…”

Conservation of core complex subunits shaped the structure and function of photosystem I in the secondary endosymbiont alga Nannochloropsis gaditana

“…The peripheral antenna is composed of light-harvesting complexes (LHC) whose sequences vary in different organisms: LHCa1-6 are present in plants (Jansson, 1999), LHCa1-9 are present in the green alga Chlamydomonas reinhardtii (Mozzo et al, 2010), whereas LHCR proteins are believed to comprise the peripheral antenna in red algae and diatoms (Busch et al, 2010;Busch & Hippler, 2011;Thangaraj et al, 2011). The number of LHC associated with PSI is also variable: four subunits are associated with the PSI core in higher plants, in the moss Physcomitrella patens, and in some red algae and diatoms (Ben-Shem et al, 2003;Veith & B€ uchel, 2007;Busch et al, 2010Busch et al, , 2013.…”

“…The number of LHC associated with PSI is also variable: four subunits are associated with the PSI core in higher plants, in the moss Physcomitrella patens, and in some red algae and diatoms (Ben-Shem et al, 2003;Veith & B€ uchel, 2007;Busch et al, 2010Busch et al, , 2013. Differently, nine antenna subunits are found associated with PSI in other red algae (Gardian et al, 2007;Thangaraj et al, 2011) as in the green alga C. reinhardtii (Drop et al, 2011).…”