Structural basis for the hyperthermostability of an archaeal enzyme induced by succinimide formation

Dongre, Aparna Vilas ; Das, Sudip ; Bellur, Asutosh ; Kumar, Sanjeev ; Chandrashekarmath, Anusha ; Karmakar, Tarak ; Balaram, Padmanabhan ; Balasubramanian, Sundaram ; Balaram, Hemalatha (2021) Structural basis for the hyperthermostability of an archaeal enzyme induced by succinimide formation Biophysical Journal, 120 (17). pp. 3732-3746. ISSN 0006-3495

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Official URL: http://doi.org/10.1016/j.bpj.2021.07.014

Related URL: http://dx.doi.org/10.1016/j.bpj.2021.07.014

Abstract

Stability of proteins from hyperthermophiles (organisms existing under boiling water conditions) enabled by a reduction of conformational flexibility is realized through various mechanisms. A succinimide (SNN) arising from the post-translational cyclization of the side chains of aspartyl/asparaginyl residues with the backbone amide -NH of the succeeding residue would restrain the torsion angle Ψ and can serve as a new route for hyperthermostability. However, such a succinimide is typically prone to hydrolysis, transforming to either an aspartyl or β-isoaspartyl residue. Here, we present the crystal structure of Methanocaldococcus jannaschii glutamine amidotransferase and, using enhanced sampling molecular dynamics simulations, address the mechanism of its increased thermostability, up to 100°C, imparted by an unexpectedly stable succinimidyl residue at position 109. The stability of SNN109 to hydrolysis is seen to arise from its electrostatic shielding by the side-chain carboxylate group of its succeeding residue Asp110, as well as through n → π∗ interactions between SNN109 and its preceding residue Glu108, both of which prevent water access to SNN. The stable succinimidyl residue induces the formation of an α-turn structure involving 13-atom hydrogen bonding, which locks the local conformation, reducing protein flexibility. The destabilization of the protein upon replacement of SNN with a Φ-restricted prolyl residue highlights the specificity of the succinimidyl residue in imparting hyperthermostability to the enzyme. The conservation of the succinimide-forming tripeptide sequence (E(N/D)(E/D)) in several archaeal GATases strongly suggests an adaptation of this otherwise detrimental post-translational modification as a harbinger of thermostability.

Item Type:Article
Source:Copyright of this article belongs to Biophysical Society.
ID Code:131283
Deposited On:06 Dec 2022 09:00
Last Modified:06 Dec 2022 09:00

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