A lysine-cysteine redox switch with an NOS bridge regulates enzyme function

Area of Science:

• Biochemistry and Molecular Biology
• Structural Biology
• Microbiology

Background:

• Cysteine residues are crucial for protein structure and function, forming disulfide bonds and participating in redox signaling.
• Oxidized cysteine species can form covalent conjugates, but regulatory switches beyond disulfides were unknown.
• Transaldolase enzymes play vital roles in cellular metabolism.

Purpose of the Study:

• To identify and characterize novel post-translational modifications regulating protein function.
• To investigate the mechanism of allosteric redox regulation in transaldolase from Neisseria gonorrhoeae.
• To explore the prevalence and potential therapeutic implications of newly discovered redox switches.

Main Methods:

• X-ray crystallography was employed to determine the protein structure in both oxidized and reduced states.
• Bioinformatic surveys of the Protein Data Bank were conducted to identify conserved motifs.
• Comparative analysis of transaldolases from various Neisseriaceae species.

Main Results:

• Discovery of a unique cysteine-lysine covalent crosslink, the NOS bridge, functioning as an allosteric redox switch in Neisseria gonorrhoeae transaldolase.
• X-ray structures revealed a 'loaded-spring' mechanism where redox activation triggers structural relaxation, increasing enzymatic activity significantly.
• The NOS bridge is conserved in related transaldolases and found in diverse protein families across all domains of life, including Homo sapiens.

Conclusions:

• The NOS bridge represents a novel class of regulatory covalent crosslinks beyond disulfide bonds.
• This redox switch mechanism dynamically controls enzyme activity through structural changes.
• The conserved nature and strategic location of the NOS bridge highlight its importance and potential as a target for drug and antibody development.