Sterol phylogenesis and algal evolution.

Abstract

The stereochemistry of several sterol precursors and end products synthesized by two fungal-like microorganisms Prototheca wickerhamii (I) and Dictyostelium discoideum (H) have been determined by chromatographic (TLC, GLC, and HPLC) and spectral (UV, MS,-and 'H NMR) methods. From I and H the following sterols were isolated from the cells : cycloartenol, cyclolaudenol, 24(28)-methylenecycloartanol, ergosterol, protothecasterol, 4a-methylergostanol, 4a-methylclionastanol, clionastanol, 2413-ethylcholesta-8,22-enol, and dictyosterol. In addition, the mechanism of C-24 methylation was investigated in both organisms by feeding to I[2-3H]lanosterol, [2-3H] Based on what is known in the literature regarding sterol distribution and phylogenesis together with our rmdings that the stereochemical outcome of squalene oxide cyclization leads to the production of cycloartenol rather than lanosterol (characteristic of the fungal genealogy) and the chirality of the C-24 alkyl group is similar in the two nonphotosynthetic microbes (Ji oriented), we conclude that Prototheca is an apoplastic Chlorelia (i.e., an alga) and that Dictyostelium as well as the other soil amoebae that synthesize cycloartenol evolved from algal rather than fungal ancestors.The sterol pathway is thought to be very ancient, perhaps having arisen during the later stages of prokaryote evolution (1, 2). True sterols-e.g., end products such as cholesterolare antedated by the production of sterol-like compoundse.g., pentacyclic triterpenoids (3-6)-which were formed in the Precambrian anaerobic environment by the cyclization of squalene. Once molecular oxygen was in sufficient quantity in the atmosphere to permit squalene oxide genesis, a switching mechanism became operative to divert squalene from pentacyclic triterpenoid production to sterol synthesis (6, 7). The first compounds derived by the anaerobic cyclization of squalene oxide are the tetracyclic stereoisomers cycloartenol and lanosterol. Neither stereoisomer is known to be formed by cyclization in the same organism, whether the latter is a prokaryote or a eukaryote (2). This bifurcation in the sterol pathway is now recognized in biochemical textbooks (8-10) and in reviews on evolution (11-13) as a means to dissociate groups of organisms with an evolutionary history of oxygenic photosynthesis-e.g., as detected through the stereospecific formation of cycloartenol and its further metabolism of the 96,19-cyclopropyl ring-from those nonphotosynthetic progenitors and their descendants, which possess a lanosterolbased pathway (2). The association of the cycloartenol route and the endosymbiotic origin and subsequent loss of the chloroplast in some nonphotosynthetic systems is not clear. The biosynthesis of cycloartenol occurs in microsomes (14) and proceeds when the chloroplast is absent (15-18). In neither case is the biosynthesis of the stereoisomer influenced by the structure of the functional steroid at the end of the pathway, and their occurrence is not influenced by the molecular clock or mutatio...

Evolutionarily conserved Δ25(27)-olefin ergosterol biosynthesis pathway in the alga Chlamydomonas reinhardtii

“…KD7PY cells accumulated trace amounts of cyclolaudenol and 24(28)-methylenecycloartanol along with minor amounts of 4 ␣ ,14 ␣ -dimethylporifersta-8,25(27)-dienol ( Table 2 ). The mass spectra of the structural isomers cyclolaudenol and 24(28)-methylenecycloartanol are almost identical to each other and, depending on the nature of the GC column, they coelute as we reported previously ( 13 ) ( Fig. 5 ).…”

“…Based on spectra of reference materials ( 31,37,38 ), the sterols from the different cell types possessed one or more functional groups of a ⌬ 22 E double bond, Relevant ions for ergosterol appeared at m /-396, 381, 378, and 363 amu and for 7-dehydroporiferasterol at m / z 410, 395, 392, and 377 amu ( Fig. 3 ) (27) -olefi n intermediate, analogous to 24 ␤ -methyl sterols in other green algae (Chlorella and Trebouxia; 22,40 ) and in the nonphotosynthetic, Chlorellalike alga Prototheca ( 13,41 ). Our results rule out the ⌬ 24 (28) olefi n pathway used in fungal ergosterol biosynthesis ( 39,42 ) because, in the fungal pathway, the methyl groups in 24-methyl and 24-ethyl sterols incorporate two and four deuterium atoms, respectively ( Fig.…”

Selective Cholinesterase Inhibitory Activities of a New Monoterpene Diglycoside and Other Constituents from Nelumbo nucifera Stamens

“…1). Through comparison of published NMR and EI-MS data, the structures of the known compounds were identified as cycloartenol (1), 35,36) p-hydroxybenzoic acid (2), 37) vanilloloside (3), 38) and 5Ј-O-methyladenosine (4). 39) This is the first report of isolation of these four, known compounds 1-4 from this plant.…”

Cytochrome P450CYP710AEncodes the Sterol C-22 Desaturase inArabidopsisand Tomato

“…It should be noted that CYP524 from a cellular slime mold (D. discoideum), containing the sequence conservation in the substrate recognition site (Figure 2), was located on the same branch of CYP710 proteins in the phylogenetic tree (Figure 9). D. discoideum produces 4a-methylergostanol, 24b-ethycholesta-8,22-enol, and dictyosterol as D 22 -sterols (Nes et al, 1990), suggesting the possibility that these different subfamily P450s may be involved in the same catalytic function. Sterol analysis indicated that the slime mold evolved from algal rather than from fungal ancestors (Nes et al, 1990), which is consistent with the close location of CYP524 and CYP710B in the phylogenetic tree (Figure 8).…”