Something stinks’: impaired hydrogen sulfide and cysteine persulfide production by cystathionine β-synthase variants identified in classical homocystinuria patients

Investigador: João B. Vicente
Auxiliary Investigator, ITQB-NOVA

This project aims to shed new lights onto the molecular basis of classical homocystinuria (CHU) due to cystathionine-β-synthase (CBS) deficiency, resulting from CBS gene mutations. The CBS canonical role in the transsulfuration branch of methionine metabolism has been increasingly extended to a major role as an endogenous source of hydrogen sulfide (H2S) source and, secondarily, cysteine persulfide (CysSSH). H2S regulates many physiological processes as a multifaceted ubiquitous signaling molecule. Disturbed H2S metabolism due to aberrant CBS expression is growingly established as an etiologic factor of several pathologies, some with clinical presentations common to CHU, namely cardiovascular disease and neurological impairment. Given that elevated plasma homocysteine does not fully explain the clinical presentations of CHU patients, impaired H2S and/or CysSSH production are likely to underlie the pathogenicity of various CBS mutations.

Abstract

Therefore, this project will comparatively characterize purified recombinant wild-type CBS and 14 pathogenic variants (located in the three structural domains) by a combination of biochemical and enzymatic assays, to compare their functional impairment in terms of the ‘canonical’, H2S-, and CysSSH-producing reactions, in the absence or presence of the exogenous pyridoxal-5’-phosphate cofactor and S-adenosyl-L-methionine (activator). Accomplishment of the proposed goals is neatly supported by the expertise of the Team on i) the production of recombinant WT CBS and pathogenic variants and ii) on their enzymatic characterization, both regarding its canonical and H2S-synthesizing reactions. Indeed, JBVicente and PLeandro have thus far published five articles focused on mechanistic aspects of CBS in relation with different pathophysiological conditions. Altogether, this project will contribute to a deeper understanding of the molecular basis of classical homocystinuria, to be further extended into cellular and in vivo studies, while supporting revising therapeutic options (currently based on dietary methionine restriction and vitamin B6 supplementation) and devising alternatives based on H2S-releasing drugs and/or dietary sources rich in polysulfides.