Twisted Schiff base intermediates and substrate locale revise transaldolase mechanism

Abstract

We examined the catalytic cycle of transaldolase (TAL) from Thermoplasma acidophilum by cryocrystallography and were able to structurally characterize--for the first time, to our knowledge--different genuine TAL reaction intermediates. These include the Schiff base adducts formed between the catalytic lysine and the donor ketose substrates fructose-6-phosphate and sedoheptulose-7-phosphate as well as the Michaelis complex with acceptor aldose erythrose-4-phosphate. These structural snapshots necessitate a revision of the accepted reaction mechanism with respect to functional roles of active site residues, and they further reveal fundamental insights into the general structural features of enzymatic Schiff base intermediates and the role of conformational dynamics in enzyme catalysis, substrate binding and discrimination. A nonplanar arrangement of the substituents around the Schiff base double bond was observed, suggesting that a structurally encoded reactant-state destabilization is a driving force of catalysis. Protein dynamics and the intrinsic hydrogen-bonding pattern appear to be crucial for selective recognition and binding of ketose as first substrate.

Carbohydrate Metabolism in Archaea: Current Insights into Unusual Enzymes and Pathways and Their Regulation

“…jannaschii has been characterized, and the crystal structure of TA from Tpl. acidophilum has been reported (127,(361)(362)(363)(364). However, in Mca.…”

Fabrication of Sb3+sensor based on 1,1′-(-(naphthalene-2,3-diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol)/nafion/glassy carbon electrode assembly by electrochemical approach

“…9 These properties are mainly due to the imine group present in Schiff bases, which could also be altered by varying the substituents in the molecules. [10][11][12] Furthermore, several studies have explored the properties of Schiff bases as catalysts, [13][14][15][16] uorescent materials, [17][18][19] electroluminescent materials, [20][21][22] etc. Since Schiff bases are known by their strong coordinative ability as a family of ligands, with the formation in most cases of 1 : 1 transition metal complexes, 23 they have been used to develop various chemosensors.…”

Protein lysine‐Nζ alkylation and O‐phosphorylation mediated by DTT‐generated reactive oxygen species

“…It remains unknown what if any the role of phosphate or phosphoryl radical is when it comes to DTT-fragment adduction at lysine N f H 3 þ groups. Interestingly, the Xray structure of a transaldolase reaction intermediate 43 shows similarities with our DTT-mediated reaction site.…”

“…Formation of Schiff bases at protein lysine N f groups is not unique. LehwessLitzmann et al 43 recently reported the X-ray structure of a transaldolase in which a Schiff base intermediate is observed at lysine K86. Our results from western blotting and MS fingerprinting also indicate that at least some serine and threonine residues, as well as possibly other oxygen-containing side chains, become phosphorylated during the DTT-mediated reaction.…”