Soluble Cyanobacterial Carotenoprotein as a Robust Antioxidant Nanocarrier and Delivery Module

Abstract

To counteract oxidative stress, antioxidants including carotenoids are highly promising, yet their exploitation is drastically limited by the poor bioavailability and fast photodestruction, whereas current delivery systems are far from being efficient. Here we demonstrate that the recently discovered nanometer-sized water-soluble carotenoprotein from Anabaena sp. PCC 7120 (termed AnaCTDH) transiently interacts with liposomes to efficiently extract carotenoids via carotenoid-mediated homodimerization, yielding violet–purple protein samples. We characterize the spectroscopic properties of the obtained pigment–protein complexes and the thermodynamics of liposome–protein carotenoid transfer and demonstrate the delivery of carotenoid echinenone from AnaCTDH into liposomes with an efficiency of up to 70 ± 3%. Most importantly, we show efficient carotenoid delivery to membranes of mammalian cells, which provides protection from reactive oxygen species (ROS). Incubation of neuroblastoma cell line Tet21N in the presence of 1 μM AnaCTDH binding echinenone decreased antimycin A ROS production by 25% (p < 0.05). The described carotenoprotein may be considered as part of modular systems for the targeted antioxidant delivery.

Microalgal protein AstaP is a potent carotenoid solubilizer and delivery module with a broad carotenoid binding repertoire

“…11A). This is consistent with the previous reports [27, 31]. Incubation of the CTDH apoprotein with AstaP(CAN) resulted in a gradual color change from orange to violet-purple, suggesting protein-protein carotenoid transfer.…”

“…However, the practical use of this protein may be limited by its carotenoid specificity, as, to our knowledge, CTDH was shown to form stable complexes only with echinenone and canthaxanthin [27,31]. Moreover, while CTDH was capable of extracting from membranes both echinenone and canthaxanthin, it could efficiently deliver only echinenone [31]. Since broadening of the repertoire of carotenoids accommodated by CTDH would be of great biomedical use, and given that AstaP can handle several carotenoids valuable to human health, we studied the possibility of carotenoid transfer from AstaP holoproteins to the CTDH apoprotein.…”

“…Such spectral changes, reflecting changes in the carotenoid microenvironment, rather unique in every carotenoprotein, has facilitated the discovery in 2017 of the protein-to-protein carotenoid transfer, which could be readily monitored by optical spectroscopy techniques [28,30]. For instance, canthaxanthin migration from the liposome membranes, where its absorbance maximum is close to 470 nm, to CTDH results in a ~90-100 nm bathochromic shift (absorbance maximum at 560-570 nm), which is accompanied by color change from orange-yellow to violet-purple [31]. Carotenoid transfer was found to be a multidirectional process.…”

“…CTDHs can extract carotenoids from the membranes and redistribute carotenoids to HCP or OCP, but can also extract carotenoids from HCP and even from OCP upon photoactivation of the latter [27]. This finding has allowed us to discover the ability of CTDH to efficiently deliver echinenone to the liposomes and the membranes of mammalian cells [31]. Moreover, such carotenoid transfer by CTDH could cause a significant antioxidative effect by preventing ROS accumulation [31].…”

“…Of note, such a success in studying OCP and related proteins became possible thanks to the ability to obtain the corresponding holoproteins upon expression in carotenoid-producing Escherichia coli cells. The first publications in 2015 [32] and 2016 [33], describing such E. coli strains, initiated an avalanche-like accumulation of articles reporting structural and mechanistic aspects of those proteins [8, 16, 18, 26-31, 33, 34].…”