Aib and Iva in the Biosphere: Neither Rare nor Necessarily Extraterrestrial

Abstract

Fourty-nine species and strains of filamentous fungi of the genera Acremonium, Bionectria, Clonostachys, Emericellopsis, Hypocrea/Trichoderma, Lecythophora, Monocillium, Nectriopsis, Niesslia, Tolypocladium, and Wardomyces, deposited with the culture collection of the Centraalbureau voor Schimmelcultures (CBS) in Utrecht, The Netherlands, were grown on nutrient agar plates. Organic extracts of mycelia were analyzed after acidic total hydrolysis and derivatization by GC/SIM-MS on Chirasil-L-Val for the presence of Aib (=alpha-aminoisobutyric acid, 2-methylalanine) and DL-Iva (=isovaline, 2-ethylalanine). In 37 of the hydrolysates, Aib was detected, and in several of them D-Iva or mixtures of D- and L-Iva. Non-proteinogenic Aib, in particular, is a highly specific marker for a distinctive group of fungal polypeptides named peptaibols or, comprehensively, peptaibiotics, i.e., peptides containing Aib and displaying (anti)biotic activities. The biotic synthesis of these amino acids by filamentous fungi contradicts the still widespread belief that alpha,alpha-dialkyl-alpha-amino acids do not or rarely occur in the biosphere and, if detected, are of extraterrestrial origin. The abundant production of peptaibiotics by cosmopolitan species of microfungi has also to be considered in the discussion on the occurrence of Aib and Iva in ancient and recent sediments. The detection of trace amounts of Aib in ice samples of Antarctica that are devoid of meteorites might also be related to the presence of Aib-producing microorganisms, being either indigenous psychrophiles, or being transported and localized by mechanisms related to bioaerosols and cryoconites. The presence of microfungi being capable of producing alpha,alpha-dialkyl alpha-amino acids in terrestrial samples, and possible contamination of extraterrestrial materials are pointed out to be of relevance for the reliable interpretation of cosmogeochemical data.

Photochirogenesis: Photochemical Models on the Origin of Biomolecular Homochirality

“…Compound specific stable isotope compositions of hydrogen, carbon, and nitrogen determined for several amino acids found in the meteorites demonstrated, that they are significantly isotopically enriched in the heavier stable isotopes compared to their terrestrial counterparts [24,65,[77][78][79][80][81][82][83]. Also in this case great analytical attention is demanded since terrestrial microorganisms could metabolize extraterrestrial nutrients with their corresponding isotopes into amino acids showing a false extraterrestrial isotopic signature [76].…”

“…Since several amino acids that were found to be enantiomerically enriched are present in the terrestrial environment, with isovaline and AIB occurring in fungal antibiotics [75,76], careful attention should be paid to excluding terrestrial contamination. Compound specific stable isotope compositions of hydrogen, carbon, and nitrogen determined for several amino acids found in the meteorites demonstrated, that they are significantly isotopically enriched in the heavier stable isotopes compared to their terrestrial counterparts [24,65,[77][78][79][80][81][82][83].…”

Configurational Assignment of D‐ and L‐Isovalines in Intact, Natural, and Synthetic Peptides by 2D‐NMR Spectroscopy

“…Current research in our laboratories is aimed at expanding the scope of this novel strategy for configurational assignment to additional Iva-containing natural peptides, and to model (and natural [9] [34 -36]) peptides characterized by other chiral C a -tetrasubstituted a-amino acids as well.…”

“…However, peptides containing l-as well as d-Iva have been recently discovered [7] [8]. Consequently, Aib and Iva enantiomers of fungal origin are not rare in the biosphere [9].…”

“…In this work, we investigated by CD the conformational preferences in solution of the other two peptides reported in the tables, namely the 16-mer integramide B (2) and its C-terminal [Pro 9,13 ] nonapeptide analogue 13 characterized by a significantly reduced amino acid sequence. The CD results obtained for peptide 2 are corroborated by a detailed 2D-NMR analysis.…”