Naslov
X-ray structural studies and molecular modelling of natural amino acid conjugates of indole-3-acetic acid (IAA)

Autori
Antolić, Snježana ; Kojić-Prodić, Biserka ; Magnus, Volker ; Klaić, Branimir

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Book of Abstracts - Programme, Eighth Croatian-Slovenian Crystallographic Meeting / Nepoznat - Zagreb : Slovensko kristalografsko društvo ; Hrvatska Kristalografska Zajednica, 1999, 37-37

Skup
Eighth Croatian-Slovenian Crystallographic Meeting

Mjesto i datum
Rovinj, Hrvatska, 17.06.1999. - 19.06.1999

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
auxin; indole-3-acetic acid; IAA; glutamine; asparagine; molecular structure; conformation; X-ray analysis; NMR spectroscopy; molecular mechanics; molecular dynamics

Sažetak
The naturally occurring amino acid conjugates of IAA (plant growth hormone, auxin) are supposed to be storage forms which are hydrolyzed to the free hormone as required for optimal plant development. To date, auxin conjugates have many times been found in plant material of various origin where they are frequently more abundant than the free hormone [J. D. Cohen & R. S. Bandurski, Ann. Rev. Plant Physiol. 33 (1982) 403]. There are physiological or pharmacological effects in plants which appear to be caused by the amino acid conjugates themselves. More detailed knowledge on their molecular structures in the solid state and in solution may provide the clue to their mechanism of action. Here we present the molecular and crystal structures of N-(IAA)-L-glutamine (1) and N-(IAA)-asparagine (2). At least compound 1 has been identified as a plant metabolite. Due to conformational flexibility of the side chain, compound 1 crystallizes with 3 conformers per asymmetric unit. X-ray structure analysis of both compounds revealed the folded conformation of the side chain tilted towards the benzene ring. The conformation of the peptide bond is trans (E). In such a hair-pin conformation (with the oxygen atoms in the carboxyl and peptide groups at the outside, and the hydrophobic atoms - aliphatic chains and the benzene ring at the inside) the molecules have amphipathic character and therefore a tendency to concentrate in liquid-aqueous phase boundaries. Crystal packing is determined by a complex three-dimensional hydrogen bond network. The same (folded) conformations were found in solution by assigning the H-1 NMR spectra on the basis of the NOEs: it was possible to identify qualitatively the conformations in solution. The X-ray and NMR-conformers were recognized as energetically favorable ones by conformational search performed by computational chemistry methods: molecular mechanics (MM) and molecular dynamics (MD). To simulate the NMR measurement conditions and to evaluate the influence of solvent on the conformational behavior of compounds 1 and 2, MD simulations were performed in methyl sulfoxide.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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