Noise-induced symmetry breaking far from equilibrium and the emergence of biological homochirality

Abstract

The origin of homochirality, the observed single-handedness of biological amino acids and sugars, has long been attributed to autocatalysis, a frequently assumed precursor for early life self-replication. However, the stability of homochiral states in deterministic autocatalytic systems relies on cross-inhibition of the two chiral states, an unlikely scenario for early life self-replicators. Here we present a theory for a stochastic individual-level model of autocatalytic prebiotic self-replicators that are maintained out of thermal equilibrium. Without chiral inhibition, the racemic state is the global attractor of the deterministic dynamics, but intrinsic multiplicative noise stabilizes the homochiral states. Moreover, we show that this noise-induced bistability is robust with respect to diffusion of molecules of opposite chirality, and systems of diffusively coupled autocatalytic chemical reactions synchronize their final homochiral states when the self-replication is the dominant production mechanism for the chiral molecules. We conclude that nonequilibrium autocatalysis is a viable mechanism for homochirality, without imposing additional nonlinearities such as chiral inhibition. DOI: 10.1103/PhysRevE.95.032407 Homochirality, the single-handedness of all biological amino acids and sugars, is one of two major universal features of life on Earth. The other is the canonical genetic code. Their universality transcends all categories of life, up to and including the three domains, and thus requires an explanation that transcends the idiosyncrasies of individual organisms and particular environments. The only universal process common to all life is, of course, evolution, and so it is natural to seek an explanation for biological homochirality in these terms, just as has been done to account for the universality and error-minimization aspects of the genetic code [1]. This paper is just such an attempt, using the simplest and most general commonly accepted attributes of living systems.The origin of biological homochirality has been one of the most debated topics since its discovery by Louis Pasteur in 1848 [2]. There are those who argue that homochirality must have preceded the first chemical systems undergoing Darwinian evolution, and there are those who believe homochirality is a consequence of life, but not a prerequisite [3]. There are even those who argue that homochirality is a consequence of underlying asymmetries from the laws of physics, invoking complicated astrophysical scenarios for the origin of chiral organic molecules [4] or even the violation of parity from the weak interactions [5,6]! In fact, explanations that are based on physical asymmetries can only predict an enantiomeric excess of one handedness over another, and not the 100% effect observed in nature [7]. * Corresponding author: fjafarpo@purdue.eduThe most influential class of theories for biological homochirality rest on an idea of F.C. Frank's, in which there is a kinetic instability of a racemic (50% right handed and 50% left handed) mi...

Proline autocatalysis in the origin of biological enantioenriched chirality

“…However, recent findings indicate that intrinsic multiplicative noise may be able to stabilize the homochiral states without crossinhibition-making nonequilbrium auto catalysis a viable mechanism of enantioenriched chirality. 11 The theory of chiral amnesia was another attempt to explain the propagation of asymmetry in solids. In short, the initial imbalance towards larger crystals of a single enantiomer drives more solid to crystallize on the larger crystal.…”

“…This inhibition may be because of the formation of an inactive heterodimer (if the initial ratio of S : R enantiomers is not 1:1, a greater fraction of the minor enantiomer will be extracted into the dimer reservoir). However, recent findings indicate that intrinsic multiplicative noise may be able to stabilize the homochiral states without cross‐inhibition—making nonequilbrium auto catalysis a viable mechanism of enantioenriched chirality …”

The Limited Roles of Autocatalysis and Enantiomeric Cross-Inhibition in Achieving Homochirality in Dilute Systems

“…In that work, Frank (1953) suggested that the interplay of autocatalysis combined with what he called mutual antagonism would be a necessary ingredient for reaching complete homochirality. Jafarpour et al (2015Jafarpour et al ( , 2017 invoked the possibility that local fluctuations could yield results that are different from those expected by solving the kinetic rate equations. Fluctuation effects are generally expected to play a role in small compartments, or when concentrations are low.…”

The Chain of Chirality Transfer as Determinant of Brain Functional Laterality. Breaking the Chirality Silence: Search for New Generation of Biomarkers; Relevance to Neurodegenerative Diseases, Cognitive Psychology, and Nutrition Science

“…The cumulative advance in chiral physics, chemistry, and mathematics sheds light on the phenomenon of chirality in general and on biological homochirality in particular. Several decades ago Frank developed the mathematical model XII for the spontaneous autocatalytic reaction as the mechanism for the evolution of homochirality [60,61]. Recently it was shown that the origin of molecular homochirality could be attributed to the non-equilibrium state of biological systems.…”

“…The diversity of stereospecific (chiral) phenomena was observed in molecular structures including chirality recognition/sensing [95,96], chirality transfer [97], chirality/helicity induction [98][99][100][101], chirality amplification [102][103][104], chirality breaking [61,105], chirality conflict [106,107], helicity inversion [108][109][110], and chiral phase transitions XVII [111][112][113][114]116]. Progress in the studies of molecular chirality transformation is helpful in resolving three questions.…”