RT Journal Article
SR Electronic
T1 Microalgal protein AstaP is a potent carotenoid solubilizer and delivery module with a broad carotenoid binding repertoire
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2021.08.05.455261
DO 10.1101/2021.08.05.455261
A1 Yury B. Slonimskiy
A1 Nikita A. Egorkin
A1 Thomas Friedrich
A1 Eugene G. Maksimov
A1 Nikolai N. Sluchanko
YR 2021
UL http://biorxiv.org/content/early/2021/08/05/2021.08.05.455261.abstract
AB Carotenoids are lipophilic substances with many biological functions, from coloration to photoprotection. Being potent antioxidants, carotenoids have multiple biomedical applications, including the treatment of neurodegenerative disorders and retina degeneration. Nevertheless, the delivery of carotenoids is substantially limited by their poor solubility in the aqueous phase. Natural water-soluble carotenoproteins can facilitate this task, necessitating studies on their ability to uptake and deliver carotenoids. One such promising carotenoprotein, AstaP (Astaxanthin-binding protein), was recently identified in eukaryotic microalgae, but its structure and functional properties remained largely uncharacterized. By using a correctly folded recombinant protein, here we show that AstaP is an efficient carotenoid solubilizer that can stably bind not only astaxanthin but also zeaxanthin, canthaxanthin, and, to a lesser extent, β-carotene, i.e. carotenoids especially valuable to human health. AstaP accepts carotenoids provided as acetone solutions or embedded in membranes, forming carotenoid-protein complexes with an apparent stoichiometry of 1:1. We successfully produced AstaP holoproteins in specific carotenoid-producing strains of Escherichia coli, proving it is amenable to cost-efficient biotechnology processes. Regardless of the carotenoid type, AstaP remains monomeric in both apo- and holoforms, while its rather minimalistic mass (∼20 kDa) makes it an especially attractive antioxidant delivery module. In vitro, AstaP transfers different carotenoids to the liposomes and to unrelated proteins from cyanobacteria, which can modulate their photoactivity and/or oligomerization. These findings expand the toolkit of the characterized carotenoid-binding proteins and outline the perspective of the use of AstaP as a unique monomeric antioxidant nanocarrier with an extensive carotenoid-binding repertoire.Competing Interest StatementThe authors have declared no competing interest.βCarβ-carotene,ASESCanalytical size-exclusion spectrochromatography,AstaPastaxanthin-binding protein,AXTastaxanthin,CANcanthaxanthin,CDcircular dichroism,CTDC-terminal domain,CTDHC-terminal domain homolog,DAdark-adapted,DADdiode array detector,HCPhelical carotenoid protein,IDintrinsically disordered,IDRintrinsically disordered region,IMACimmobilized metal-affinity chromatography,IPTGisopropyl-β-thiogalactoside,LAlight-adapted,LEDlight-emitting diode,NMRnuclear magnetic resonance,NTDN-terminal domain,OCPorange carotenoid protein,OCPOthe orange dark-adapted form of OCP,OCPRthe red light-adapted form of OCP,ROSreactive oxygen species,SDS-PAGEsodium dodecyl sulfate-polyacrylamide gel electrophoresis,SECsize-exclusion chromatography,SEC-MALSsize-exclusion chromatography coupled to multi-angle light scattering,ZEAzeaxanthin.