Structural insight into the molecular mechanism of allosteric activation of human cystathionine β-synthase by S -adenosylmethionine

Abstract

Significance Cystathionine β-synthase (CBS), the pivotal enzyme of the transsulfuration pathway, regulates flux through the pathway to yield compounds, such as cysteine, glutathione, taurine, and H 2 S, that control cellular redox status and signaling. Our crystal structure of an engineered human CBS construct bound to S -adenosylmethionine (AdoMet) reveals the unique binding site of the allosteric activator and the architecture of the human CBS enzyme in its activated conformation. Together with the basal conformation that we reported earlier, these structures unravel the molecular mechanism of human CBS activation by AdoMet. Current knowledge will allow for modeling of numerous pathogenic mutations causing inherited homocystinuria and for design of compounds modulating CBS activity.

Allosteric control of human cystathionine β-synthase activity by a redox active disulfide bond

“…In addition to the mass spectrometry, methyl-PEG 24 -maleimide (MM[PEG] 24 ) was used to label the thiols of the oxidized and reduced CBS. The difference between the molecular weights of the labeled oxidized and reduced forms of CBS was ~3 kDa (Fig.…”

“…Additionally, a structural role for the heme in the proper folding of CBS has been described (21). The C-terminal domain contains a tandem of the so-called CBS domain, which forms a regulatory domain that binds S-adenosylmethionine (SAM), an allosteric activator (22)(23)(24). Cleavage of the regulatory domain from full-length CBS yields a truncated dimeric enzyme that is more active than full-length CBS but is unresponsive to SAM (25).…”

Enzyme replacement with PEGylated cystathionine β-synthase ameliorates homocystinuria in murine model

“…This form of the enzyme has a high tendency toward aggregation, which poses a major constraint on purification efforts (13). Additionally, CBS is allosterically regulated by S-adenosyl-methionine (SAM), which binds to the autoinhibitory C-terminal regulatory domain and activates the enzyme by approximately 5-fold in vitro (14). SAM levels in CBS-deficient patients and controls are 1.38 μM and 0.093 μM, respectively (15), in both cases far below the K act value for CBS (17.7 μM) (16), which would prevent full activation of hCBS if administered to patients.…”

S-Adenosyl-l-methionine Modulates CO and NO• Binding to the Human H2S-generating Enzyme Cystathionine β-Synthase

“…An increasing number of structural and functional data have been reported over the past few years to elucidate the molecular mechanism of CBS activation by AdoMet (11,12,26,30,31). Two AdoMet-binding sites with different affinity and distinct functional and structural roles have been proposed (26).…”

“…The crystallographic structure of the full-length human CBS with all three domains shows that in the absence of AdoMet the C-terminal domain reduces the substrate accessibility to the PLP site in the catalytic core (11). Conversely, the structure obtained in the presence of AdoMet shows that, upon AdoMet binding, two C-terminal domains from adjacent monomers associate, thereby increasing the active site accessibility and in turn the enzyme activity (12). This model is further supported by the observation that the truncated C-terminal regulatory domain (lacking the first 405 residues composing the N-terminal and catalytic domains) assembles as a dimer in the presence of AdoMet (31).…”