Structural basis of regulation and oligomerization of human cystathionine β-synthase, the central enzyme of transsulfuration

Abstract

Cystathionine β-synthase (CBS) controls the flux of sulfur from methionine to cysteine, a precursor of glutathione, taurine, and H 2 S. CBS condenses serine and homocysteine to cystathionine with the help of three cofactors, heme, pyridoxal-5′-phosphate, and S-adenosyl-L-methionine. Inherited deficiency of CBS activity causes homocystinuria, the most frequent disorder of sulfur metabolism. We present the structure of the human enzyme, discuss the unique arrangement of the CBS domains in the C-terminal region, and propose how they interact with the catalytic core of the complementary subunit to regulate access to the catalytic site. This arrangement clearly contrasts with other proteins containing the CBS domain including the recent Drosophila melanogaster CBS structure. The absence of large conformational changes and the crystal structure of the partially activated pathogenic D444N mutant suggest that the rotation of CBS motifs and relaxation of loops delineating the entrance to the catalytic site represent the most likely molecular mechanism of CBS activation by S-adenosyl-L-methionine. Moreover, our data suggest how tetramers, the native quaternary structure of the mammalian CBS enzymes, are formed. Because of its central role in transsulfuration, redox status, and H 2 S biogenesis, CBS represents a very attractive therapeutic target. The availability of the structure will help us understand the pathogenicity of the numerous missense mutations causing inherited homocystinuria and will allow the rational design of compounds modulating CBS activity.

Human 60-kDa Lysophospholipase Contains an N-terminal l-Asparaginase Domain That Is Allosterically Regulated by l-Asparagine

“…4C). As the shift between oligomeric states of enzymes can be drastically influenced by their substrates and/or other interacting partners (45,46), we decided to perform gel filtration analysis in the presence of the substrate of hASNase1. Interestingly, with 20 mM L-Asn in the running buffer, we witnessed a slightly shifted shoulder peak of the previously observed chromatographic peak assigned to the 40-kDa hASNase1 monomer, indicative of a higher molecular weight species, although the monomer remained the predominant form (Fig.…”

The Therapeutic Potential of Cystathionine β-Synthetase/Hydrogen Sulfide Inhibition in Cancer

“…1). A truncated form of CBS (a 45 kDa ''active core'') that exhibits increased catalytic activity due to a loss of the Cterminal CBS motifs has also been described (28,58,148).…”

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).…”

“…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).…”