Table 2.
Exaptation of small molecules
| Molecule | Ancestral functiona | Exapted function(s) |
|---|---|---|
| Adenosine (Kanatani and Hiramoto 1970; De Crombrugghe et al. 1984; Hanks and Hunter 1995; Ciruela et al. 2006) | Component of RNA | Energy source (ATP, coenzyme A), redox cofactor (NAD, FAD), regulator of the lac operon, activator of protein kinase A, neurotransmitter, and hormone |
| Citrate (Iacobazzi and Infantino 2014; Williams and O’Neill 2018; Granchi et al. 2019) | Intermediate in the Krebs cycle | Fatty acid biosynthesis, sterol biosynthesis, metabolic regulation, metal coordination, component of bone, inflammation, insulin secretion, histone acetylation, prostatic cell function, and carbon source (anaerobic bacteria) |
| Beta-carotene (Pryor et al. 2000; Dieser et al. 2010; Cazzonelli 2011; Kirti et al. 2014) | Survival in cold environments | Precursor of Vitamin A, light-harvesting pigment, photo-protection, glycoprotein synthesis, protection from oxidation, and pollinator attractant |
| Riboflavin (Rajamani et al. 2008; Dakora et al. 2015; Sepúlveda Cisternas et al. 2018) | Electron transport | Reduction of glutathione, production of pyridoxic acid, α-ketoglutarate, branched-chain amino acids, and fatty acids, oxidation of pyruvate, conversion of retinol to retinoic acid bacterial pigment, coenzyme (vitamin B2), anti-oxidant inducer (plants), induction of disease resistance (plants), and quorum sensing (AHL mimic) |
| Pterins (Basu and Burgmayer 2011) | Pigments | Electron transfer cofactors, redox cofactors, precursor of folates, and toxins |
| GABA (Gamma-aminobutyric acid) (Moore and Speh 1993; Bouche and Fromm 2004; Feehily and Karatzas 2013) | Stress response in bacteria | Inhibitory neurotransmitter in vertebrates, and signaling molecule and metabolite in plants |
| Sterols (Gil et al. 2018), (de Jong et al. 2003) | Membrane fluidity | Metabolite precursors, growth regulator (plants), calcium absorption (Vitamin D), transcription regulator (progesterone), and cell signaling |
| Guanosine (Mellion et al. 1981; Frizzo et al. 2001) | Component of RNA | Glutamate regulator, inhibitor of platelet aggregation, second messenger, alarmone in bacteria, and energy source for translation |
| Lactate (Sola‐Penna 2008; Proia et al. 2016) | Energy source (fermentation) | Signaling molecule (brain), muscle glycogen production, and spermatogenesis |
aThe term “function” here is equivalent to “character” in reference (Stevens 1980). Ancestry is relative to more recent exapted functions and should not be interpreted to imply ultimate ancestry