Biological functions of carotenoids ‐ diversity and evolution

Abstract

Carotenoids first emerged in archaebacteria as lipids reinforcing cell membranes. To serve this function their long molecules have extremely rigid backbone due to the linear chain of usually 10 to 11 conjugated C=C bonds in transconfiguration--the length corresponding the thickness of hydrophobic zone of membrane which they penetrate as "molecular rivets". Carotenoids retain their membrane-reinforcing function in some fungi and animals. The general structure of carotenoid molecule, originally having evolved for mechanical functions in membranes, possess a number of other properties that were later used for independent functions. The most striking fact is that these properties proved to fit some new functions to perfection. The polyene chain of 9-11 double bonds absorbs light precisely in the gap of chlorophyll absorption--function as accessory light-harvesting pigments in all plants; Unique arrangement of electronic levels owing to the by polyene chain structure makes carotenoids the only natural compounds capable of excitation energy transfer both (i) from carotenoid excited state to chlorophyll in the light-harvesting complex and (ii) from triplet chlorophyll or singlet oxygen to carotenoid in photosynthetic reaction centers--protection of RC from photodamage. The linear system of conjugated C=C bonds provides high reducing potential of carotenoid molecules making them potent antioxidants in lipid formations. Still, there is a lack of evidence of the chemical antioxidant function of carotenoids, especially in higher organisms; most data demonstrate an antioxidant ability rather than a function. Carotenoids have many other independent biological functions, including: specific coloration patterns in plants and animals, screening from excessive light and spectral filtering, defense of egg proteins from proteases in some invertebrates; the direct carotenoid derivative--retinal--acts as visual pigment in all animals and as chromophore in bacteriorhodopsin photosynthesis, retinoic acid in animals and abscisic acid in plants serve as hormones. All these functions utilize various properties (mechanical, electronic, stereospecific) of a single structure evolved in bacteria for a single membrane-reinforcing function, thus demonstrating an example of pure evolutionary preadaptation. One of the practical conclusions that can be reached by reviewing uniquely diverse properties and functions of carotenoids is that, when considering possible mechanisms of their effects in organisms (e.g., anticarcinogenic action), all their functional traits should be taken into account.

Could Fucoxanthin Interaction with Lipid Rafts Mediate its Cytotoxicity in Cancer Cells?

“…Structure and biological activity of fucoxanthin and carotenoids in cancer cells [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Biological functions of carotenoids in cell membranes [19][20][21][22] Interaction of carotenoids with lipid rafts [23] Cell model to study the integration of xenobiotics into lipid rafts [24] Antioxidant and pro-oxidant activity of fucoxanthin in animal cells and tissues [25][26][27] Structure and function of lipid rafts in cell membranes [28,29] Targeting lipid rafts in cancer cells [30][31][32][33][34][35][36] Ion channels, lipid rafts and cancer cells [37,38] Lipid rafts, cytoskeleton, cancer cells invasivity and tumor angiogenesis [30,40] …”

“…In support of this hypothesis, fucoxanthin contains two polar heads, separated by a polyene chain, that confer to the molecule a bolaphile behaviour and the appropriate size for its integration into plasma and intracellular membranes. Accordingly, it is assumed that the first evolutionary function of carotenoids was to rigidify the cell membranes of archaebacteria [20]. In algae, fucoxanthin locates in thylakoid membranes where it is tightly bound to chlorophyll molecules and apoproteins to form functional lightharvesting complexes [21].…”

Pigments and Pathogenesis

“…In higher animals colour can signal sexual fitness as brightly coloured birds attest to [1]. But pigments can serve a more fundamental purpose that includes protection from oxidative stress, absorption of light in plants and the retina in animals, and protection from harmful UV light [1].…”

“…In higher animals colour can signal sexual fitness as brightly coloured birds attest to [1]. But pigments can serve a more fundamental purpose that includes protection from oxidative stress, absorption of light in plants and the retina in animals, and protection from harmful UV light [1]. The appearance to have colour may be incidental to the chemistry of these pigments which contain varying amounts of conjugated double bonds [1].…”

“…But pigments can serve a more fundamental purpose that includes protection from oxidative stress, absorption of light in plants and the retina in animals, and protection from harmful UV light [1]. The appearance to have colour may be incidental to the chemistry of these pigments which contain varying amounts of conjugated double bonds [1]. These double bonds serve to absorb light which leads to the phenomenon of colour.…”