Prebiotic Iron Originates the Peptidyl Transfer Origin

IRES-mediated Pichia pastoris cell-free protein synthesis

Cell-free protein synthesis (CFPS) system is an ideal platform for fast and convenient protein research and has been used for macromolecular assembly, unnatural amino acid embedding, glycoprotein production, and more. To realize the construction of an efficient eukaryotic CFPS platform with the advantages of low cost and short time, a CFPS system based on the yeast Pichia pastoris was built in this study. The internal ribosomal entry site (IRES) can independently initiate translation and thus promote protein synthesis. The Kozak sequences can facilitate translation initiation. Therefore, the screening of IRES and its combination with Kozak was performed, in which cricket paralysis virus (CRPV) exhibited as the best translation initiation element from 14 different IRESs. Furthermore, the system components and reaction environment were explored. The protein yield was nearly doubled by the addition of RNase inhibitor. The cell extract amount, energy regeneration system (phosphocreatine and phosphocreatine kinase), and metal ions (K+ and Mg2+) were optimized to achieve the best protein synthesis yield. This P. pastoris CFPS system can extend the eukaryotic CFPS platform, providing an enabling technology for fast prototyping design and functional protein synthesis.

Reconsidering the czcD (NiCo) Riboswitch as an Iron Riboswitch

Recent work has proposed a new mechanism of bacterial iron regulation: riboswitches that undergo a conformational change in response to Fe^II. The czcD (NiCo) riboswitch was initially proposed to be specific for Ni^II and Co^II, but we recently showed via a czcD-based fluorescent sensor that Fe^II is also a plausible physiological ligand for this riboswitch class. Here, we provide direct evidence that this riboswitch class responds to Fe^II. Isothermal titration calorimetry studies of the native czcD riboswitches from three organisms show no response to Mn^II, a weak response to Zn^II, and similar dissociation constants (∼1 μM) and conformational responses for Fe^II, Co^II, and Ni^II. Only the iron response is in the physiological concentration regime; the riboswitches’ responses to Co^II, Ni^II, and Zn^II require 10³-, 10⁵-, and 10⁶-fold higher “free” metal ion concentrations, respectively, than the typical availability of those metal ions in cells. By contrast, the “Sensei” RNA, recently claimed to be an iron-specific riboswitch, exhibits no response to Fe^II. Our results demonstrate that iron responsiveness is a conserved property of czcD riboswitches and clarify that this is the only family of iron-responsive riboswitch identified to date, setting the stage for characterization of their physiological function.

Cutting in-line with iron: ribosomal function and non-oxidative RNA cleavage

Divalent metal cations are essential to the structure and function of the ribosome. Previous characterizations of the ribosome performed under standard laboratory conditions have implicated Mg²⁺ as a primary mediator of ribosomal structure and function. Possible contributions of Fe²⁺ as a ribosomal cofactor have been largely overlooked, despite the ribosome's early evolution in a high Fe²⁺ environment, and the continued use of Fe²⁺ by obligate anaerobes inhabiting high Fe²⁺ niches. Here, we show that (i) Fe²⁺ cleaves RNA by in-line cleavage, a non-oxidative mechanism that has not previously been shown experimentally for this metal, (ii) the first-order in-line rate constant with respect to divalent cations is >200 times greater with Fe²⁺ than with Mg²⁺, (iii) functional ribosomes are associated with Fe²⁺ after purification from cells grown under low O₂ and high Fe²⁺ and (iv) a small fraction of Fe²⁺ that is associated with the ribosome is not exchangeable with surrounding divalent cations, presumably because those ions are tightly coordinated by rRNA and deeply buried in the ribosome. In total, these results expand the ancient role of iron in biochemistry and highlight a possible new mechanism of iron toxicity.

Root of the Tree: The Significance, Evolution, and Origins of the Ribosome

The ribosome is an ancient molecular fossil that provides a telescope to the origins of life. Made from RNA and protein, the ribosome translates mRNA to coded protein in all living systems. Universality, economy, centrality and antiquity are ingrained in translation. The translation machinery dominates the set of genes that are shared as orthologues across the tree of life. The lineage of the translation system defines the universal tree of life. The function of a ribosome is to build ribosomes; to accomplish this task, ribosomes make ribosomal proteins, polymerases, enzymes, and signaling proteins. Every coded protein ever produced by life on Earth has passed through the exit tunnel, which is the birth canal of biology. During the root phase of the tree of life, before the last common ancestor of life (LUCA), exit tunnel evolution is dominant and unremitting. Protein folding coevolved with evolution of the exit tunnel. The ribosome shows that protein folding initiated with intrinsic disorder, supported through a short, primitive exit tunnel. Folding progressed to thermodynamically stable β-structures and then to kinetically trapped α-structures. The latter were enabled by a long, mature exit tunnel that partially offset the general thermodynamic tendency of all polypeptides to form β-sheets. RNA chaperoned the evolution of protein folding from the very beginning. The universal common core of the ribosome, with a mass of nearly 2 million Daltons, was finalized by LUCA. The ribosome entered stasis after LUCA and remained in that state for billions of years. Bacterial ribosomes never left stasis. Archaeal ribosomes have remained near stasis, except for the superphylum Asgard, which has accreted rRNA post LUCA. Eukaryotic ribosomes in some lineages appear to be logarithmically accreting rRNA over the last billion years. Ribosomal expansion in Asgard and Eukarya has been incremental and iterative, without substantial remodeling of pre-existing basal structures. The ribosome preserves information on its history.