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  • Title: Crystal structure of cystathionine β-synthase from honeybee Apis mellifera.
    Author: Giménez-Mascarell P, Majtan T, Oyenarte I, Ereño-Orbea J, Majtan J, Klaudiny J, Kraus JP, Martínez-Cruz LA.
    Journal: J Struct Biol; 2018 Apr; 202(1):82-93. PubMed ID: 29275181.
    Abstract:
    Cystathionine β-synthase (CBS), the key enzyme in the transsulfuration pathway, links methionine metabolism to the biosynthesis of cellular redox controlling molecules. CBS catalyzes the pyridoxal-5'-phosphate-dependent condensation of serine and homocysteine to form cystathionine, which is subsequently converted into cysteine. Besides maintaining cellular sulfur amino acid homeostasis, CBS also catalyzes multiple hydrogen sulfide-generating reactions using cysteine and homocysteine as substrates. In mammals, CBS is activated by S-adenosylmethionine (AdoMet), where it can adopt two different conformations (basal and activated), but exists as a unique highly active species in fruit fly Drosophila melanogaster. Here we present the crystal structure of CBS from honeybey Apis mellifera, which shows a constitutively active dimeric species and let explain why the enzyme is not allosterically regulated by AdoMet. In addition, comparison of available CBS structures unveils a substrate-induced closure of the catalytic cavity, which in humans is affected by the AdoMet-dependent regulation and likely impaired by the homocystinuria causing mutation T191M.
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