The Origin and Early Evolution of Life: Homochirality Emergence in Prebiotic Environments.

Homochirality is one of the signatures of life. Numerous geological and prebiotic chemistry studies have proved that disordered soups containing small organic molecules, gases, liquids, and minerals (such as those containing phosphorous) yielded racemic mixtures of building blocks for biomolecule assembly. Polymers obtained from these bricks should have been enantiopure with functional properties similar to modern biomolecules or heterochiral with some functions such as catalyzing a chemical transformation unspecifically. Up until now, no clues have been found as to how symmetry breaking occurred. In this review, we highlight the principal achievements regarding the emergence of homochirality during the prebiotic synthesis of building blocks. Furthermore, we tried to focus on approaches based on prebiotic systems chemistry (bottom-up) and laboratory scales to simulate plausible prebiotic messy environments for the emergence of life. We aim with this review to assemble, even partially, the puzzle pieces of the origin of life regarding the relevant phenomenon of homochiral symmetry breaking.

Microwave-Assisted Syntheses of Rhodamine, Rhodol, and Fluorescein Derivatives.

A series of rhodol-; fluorescein- and rhodamines-based spirolactam compounds, bearing electron donor amines have been prepared. For this purpose we have redesigned the synthesis of the rhodol scaffold using 2-(2,4-dihydroxybenzoyl)benzoic acid obtaining one example rhodol methyl ester in good yields (25-30 %) Thus, one set of non-cytotoxic rhodamine-based compounds has been prepared using thermal and microwave assisted synthesis (40-78 %) and tested as high affinity ATP chemo-sensors.

Comprehensive Characterization of an "Off/On" Rhodol-Based Lysosomal Tracker for Orthogonal Cellular Analysis by Confocal Imaging.

Two florescent xanthene-cyanamide lysosomal trackers emitting strongly at ∼525 nm were prepared from fluorescein and rhodol methyl esters in microwave-assisted reactions. Both forms named "off" (nonfluorescent lactam) and "on" (strongly fluorescent ring-opened amide) have been comprehensively characterized out by using a combination of NMR spectroscopy, X-ray analysis, fluorimetry and confocal microscopy. Known rhodamines bearing electron-withdrawing groups (EWGs) exhibit an equilibrium between non-fluorescent (off) and fluorescent (on) depending on the dielectric constant of the medium. Here, cyanamide was introduced as EWG amine into the fluorescein and rhodol framework. Unlike rhodamine-type dyes, the ring-opened forms of fluorescein- and rhodol-cyanamides are stable in protic solvents under circumneutral and basic pH conditions. The osteoblastic cell line MC3T3-E1 from C57BL/6 mouse calvaria was used for confocal imaging where the different organelles and nuclei were distinguished by using an orthogonal combination of fluorescent dyes.

Shedding Light on the Role of Na,K-ATPase as a Phosphatase during Matrix-Vesicle-Mediated Mineralization.

Matrix vesicles (MVs) contain the whole machinery necessary to initiate apatite formation in their lumen. We suspected that, in addition to tissue-nonspecific alkaline phosphatase (TNAP), Na,K,-ATPase (NKA) could be involved in supplying phopshate (Pi) in the early stages of MV-mediated mineralization. MVs were extracted from the growth plate cartilage of chicken embryos. Their average mean diameters were determined by Dynamic Light Scattering (DLS) (212 ± 19 nm) and by Atomic Force Microcopy (AFM) (180 ± 85 nm). The MVs had a specific activity for TNAP of 9.2 ± 4.6 U·mg-1 confirming that the MVs were mineralization competent. The ability to hydrolyze ATP was assayed by a colorimetric method and by 31P NMR with and without Levamisole and SBI-425 (two TNAP inhibitors), ouabain (an NKA inhibitor), and ARL-67156 (an NTPDase1, NTPDase3 and Ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) competitive inhibitor). The mineralization profile served to monitor the formation of precipitated calcium phosphate complexes, while IR spectroscopy allowed the identification of apatite. Proteoliposomes containing NKA with either dipalmitoylphosphatidylcholine (DPPC) or a mixture of 1:1 of DPPC and dipalmitoylphosphatidylethanolamine (DPPE) served to verify if the proteoliposomes were able to initiate mineral formation. Around 69-72% of the total ATP hydrolysis by MVs was inhibited by 5 mM Levamisole, which indicated that TNAP was the main enzyme hydrolyzing ATP. The addition of 0.1 mM of ARL-67156 inhibited 8-13.7% of the total ATP hydrolysis in MVs, suggesting that NTPDase1, NTPDase3, and/or NPP1 could also participate in ATP hydrolysis. Ouabain (3 mM) inhibited 3-8% of the total ATP hydrolysis by MVs, suggesting that NKA contributed only a small percentage of the total ATP hydrolysis. MVs induced mineralization via ATP hydrolysis that was significantly inhibited by Levamisole and also by cleaving TNAP from MVs, confirming that TNAP is the main enzyme hydrolyzing this substrate, while the addition of either ARL-6715 or ouabain had a lesser effect on mineralization. DPPC:DPPE (1:1)-NKA liposome in the presence of a nucleator (PS-CPLX) was more efficient in mineralizing compared with a DPPC-NKA liposome due to a better orientation of the NKA active site. Both types of proteoliposomes were able to induce apatite formation, as evidenced by the presence of the 1040 cm-1 band. Taken together, the findings indicated that the hydrolysis of ATP was dominated by TNAP and other phosphatases present in MVs, while only 3-8% of the total hydrolysis of ATP could be attributed to NKA. It was hypothesized that the loss of Na/K asymmetry in MVs could be caused by a complete depletion of ATP inside MVs, impairing the maintenance of symmetry by NKA. Our study carried out on NKA-liposomes confirmed that NKA could contribute to mineral formation inside MVs, which might complement the known action of PHOSPHO1 in the MV lumen.

Synthesis of Phospholipids Under Plausible Prebiotic Conditions and Analogies with Phospholipid Biochemistry for Origin of Life Studies.

Phospholipids are essential components of biological membranes and are involved in cell signalization, in several enzymatic reactions, and in energy metabolism. In addition, phospholipids represent an evolutionary and non-negligible step in life emergence. Progress in the past decades has led to a deeper understanding of these unique hydrophobic molecules and their most pertinent functions in cell biology. Today, a growing interest in "prebiotic lipidomics" calls for a new assessment of these relevant biomolecules.