2014 Annual Science Report
University of Illinois at Urbana-Champaign Reporting | SEP 2013 – DEC 2014
Project 2: Cells as Engines and the Serpentinization Hypothesis for the Origin of Life
All life is, and must be, “powered” since all of its most essential and distinguishing processes have to be driven “up-hill” against their natural thermodynamic direction. By the 2nd law of thermodynamics, however, a process can only be made to proceed up-hill by being mechanistically linked, via a molecular device functioning as an engine, to another, more powerful, process that is moving in its natural, down-hill direction. On fundamental principles, we argue, such engine-mediated conversion activities must also have been operating at, and indeed have been the cause of, life’s emergence. But what then were life’s birthing engines, what sources of power drove them, what did they need to produce, and how did they arise in an entirely lifeless world? Promising potential answers to these and other questions related to the emergence of life are provided by the Alkaline Hydrothermal Vent/serpentinization (“AHV”) hypothesis, whose original propounder and lead proponent, Dr. Michael Russell of JPL, is a co-investigator on this project. The goal of the project is specifically to clarify the essential mechanistic modus operandi of all molecular engines that power life, and to see how the most fundamental and prerequisite of these could have arisen, and operated, in the structures and flows produced by the serpentinization process. Importantly, candidate answers to these questions can be put to definitive laboratory tests.
Interest in the AHV/serpentinization model for the emergence of life derives mainly from the fact that the alkaline vents produced by serpentinization acting in an ocean floor can generate precipitate structures that are seemingly ideal incubators for life’s genesis. Comprised of immense labyrinthine arrays of mineral-membrane-bound microchambers, these structures, in the Hadean epoch, would have formed a kind of abiotic stromatolite whose “cells” were richly supplied by the operating geochemistry, and thus “for free”, with a full-fledged ambient, transmembrane protonmotive force and a suite of life-appropriate redox gradients – and thus could have functioned as minimalist “mineral-mitochondria”. Further, the membranes of these mineral-mitochondrial cells husband specific transition-metal sulfide and oxyhydride complexes (closely comparable to some of the active centers of modern enzymes doing similar work) could then have enabled molecular engines capable of coupling the external, geochemically-given disequilibria to the internal endergonic reactions necessary to initiate the emergence of life: e.g. the production of pyrophosphate (the precursor to ATP as a free energy carrier) from orthophosphate and the fixation of carbon from CO2 and of nitrogen (as ammonium) from nitrate. No “soup” this, but a highly dynamic and organized, and self-organizing, engine-powered rocketship; one which, in one place and time, achieved “ignition” and then, autocatalytically, lifted off – bringing the planet to life.
The challenge, of course, is to prove it; and the key step is to catch the proposed abiotic engines in the act. Efforts to address this challenge are now underway at a number of centers (e.g., UC London and the RIKEN Center, Japan), but are somewhat hampered, we believe, by confusion regarding how molecular engines, i.e. processes that can convert one disequilibria (e.g. a redox gradient) into another (e.g. fixed carbon) actually function. It is widely held that these processes are just (electro) chemical reactions, and that therefore what we need find in the abiotic world are catalysts that can mediate these reactions. But this is incorrect; such processes are not just chemical reactions, and they need devices to mediate them that are not just acting as catalysts. What they require are true molecular engines.
Our work with Michael Russell over the last few years, the last year in particular, has focused in large part on an effort to explicate this specific issue, and to use that understanding to guide experimental attempts at model validation. The essential point at issue is that molecular engines are fundamentally Brownian ratchets controlled by an escapement mechanism. The escapement’s purpose is to ensure that an instance of the driven, up-hill reaction, itself produced by Brownian fluctuations, “gates” (i.e. allows to go to completion) an instance of the quasi-irreversible driving reaction; this then “traps” the driven reaction, in effect permitting only favorable (i.e. “rectifying”) Brownian fluctuations in a 2nd-law consistent manner, and allowing work to be done. We have recently developed a conceptual and statistical-physics model of such escapement-mechanism-mediated disequilibrium conversion processes. We argue that this model can stand as a “Turing Machine” abstraction, capturing, in their simplest possible realization, the essential and universal features of all molecular engine devices – and which, thereby, describes an enabling, and indeed universal, property of life. This work was first presented, by Branscomb (co-author Russell), at the recent TDE Focus Group meeting in Tokyo mentioned below. The first paper to be based on it, which is to be authored by all four members of this project, is under active preparation.
In January, 2014, Branscomb, Goldenfeld, and Russell attended the Origins of Life Gordon Conference In Galveston, where Branscomb, with co-author Russell, presented a poster on life and non-equilibrium thermodynamics, and Russell was an invited speaker. Also in January, Branscomb and Goldenfeld participated in a meeting on the origin of life at ELSI in Tokyo, at which Goldenfeld spoke on the challenges entailed in developing an understanding of the universal principles underpinning life and Branscomb gave a brief oral presentation that essentially summarized the content of the Gordon Conf. Poster.
In November, Branscomb, along with Russell, attended, as invited participants, the 13th meeting of the NAI Thermodynamics, Disequilibria, and Evolution Focus Group which took place at the ELSI in Tokyo. At that meeting Branscomb presented a talk based on the escapement mechanism model (“_Disequilibria; the cause of all things_”) and Russell presented one of the meeting’s two major lectures “_Driving the very first steps to metabolism_”.
Finally, in 2014, Russell and co-authors (including Branscomb) published a major review and status report on the AHV/serpentinizatin model (cited below) titled “_The Drive to Life on Wet and Icy Worlds_”, which appeared as the cover article in the journal Astrobiology, v14, #4.
PROJECT MEMBERS:Elbert Branscomb
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Sources of prebiotic materials and catalysts
Origins and evolution of functional biomolecules
Origins of energy transduction
Origins of cellularity and protobiological systems