7d40
Crystal structure of GATase subunit of Methanocaldococcus jannaschii GMP synthetase
Structural highlights
FunctionGUAAA_METJA Catalyzes the synthesis of GMP from XMP (By similarity). Publication Abstract from PubMedStability 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 Psi and can serve as a new route for hyperthermostability. However, such a succinimide is typically prone to hydrolysis, transforming to either an aspartyl or beta-isoaspartyl residue. Here, we present the crystal structure of Methanocaldococcus jannaschii glutamine amidotransferase (MjGATase) and using enhanced sampling molecular dynamics simulations, address the mechanism of its increased thermostability, up to 100 (o)C, imparted by an unexpectedly stable succinimidyl residue (SNN) 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-->pi( *) 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 alpha-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 Phi-restricted prolyl residue highlights the specificity of the succinimidyl residue in imparting hyperthermostability to the enzyme. The conservation of 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. Structural basis for the hyperthermostability of an archaeal enzyme induced by succinimide formation.,Dongre AV, Das S, Bellur A, Kumar S, Chandrashekarmath A, Karmakar T, Balaram P, Balasubramanian S, Balaram H Biophys J. 2021 Jul 21. pii: S0006-3495(21)00600-7. doi:, 10.1016/j.bpj.2021.07.014. PMID:34302792[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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