H2S biogenesis by cystathionine beta-synthase: mechanism of inhibition by aminooxyacetic acid and unexpected role of serine

• DOI: 10.1007/s00018-022-04479-9
• Publication Date: 2022-07-21T22:02:23Z
• Authors: Maria Petrosino; Karim Zuhra; Jola Kopec; Andrew Hutchin; Csaba Szabo; Tomas Majtan
• Keywords: Aminooxyacetic acid; Cystathionine gamma-lyase

Cystathionine beta-synthase (CBS) is a pivotal enzyme of the transsulfuration pathway responsible for diverting homocysteine to biosynthesis cysteine and production hydrogen sulfide (H2S). Aberrant upregulation CBS overproduction H2S contribute pathophysiology several diseases including cancer Down syndrome. Therefore, pharmacological inhibition has emerged as prospective therapeutic approach. Here, we characterized binding inhibitory mechanism aminooxyacetic acid (AOAA), most commonly used inhibitor. We found that AOAA binds tighter than its respective substrates forms dead-end PLP-bound intermediate featuring an oxime bond. Surprisingly, serine, but not cysteine, replaced from formed aminoacrylate reaction intermediate, which allowed continuation catalytic cycle. Indeed, serine rescued essentially normalized enzymatic activity AOAA-inhibited CBS. Cellular studies confirmed decreased bioenergetics, while additional activity, mitochondrial function. The crystal structure AOAA-bound human showed lack bonding with residues G305 Y308, in serine-bound model. Thus, could be reactivated by serine. This difference may important cellular environment multiple pathophysiological conditions modulate CBS-inhibitory AOAA. In addition, our results demonstrate complexities using CBS-specific inhibitor biogenesis point urgent need develop potent, selective specific