Cystathionine gamma-lyase (CSE) is a member of the gamma family of PLP-dependent enzymes (which bind to pyridoxal-5'-phosphate for reaction catalysis), along with other enzymes such as cystathionine gamma-synthase, Cystathionine beta-lyase, and Methionine gamma-lyase. Similar to other enzymes in this family, CSE exhibits a tetrameric structure with D2 symmetry.
Functions
Cystathionine gamma-lyase serves two primary functions in Homo sapiens: one is associated with the conversion of L,L-cystathionine into L-cysteine, while the other is linked to the synthesis of H2S (hydrogen sulfide), a signaling molecule implicated in neurological and vascular processes [1].
CSE operates in conjunction with cystathionine beta-synthase (CBS) to facilitate the reverse transsulfuration required for the metabolic interconversion of sulfur-containing amino acids, such as cysteine. Remarkably, reverse transsulfuration is a process exclusive to fungi and mammals. In this intricate process, CBS enzymatically catalyzes the formation of cystathionine from the precursor molecules, homocysteine and serine. Subsequently, CSE mediates the conversion of the synthesized cystathionine into cysteine, alpha-ketobutyrate, and ammonia [2].
.CSE also assumes the responsibility for the synthesis of H2S in mammals. This production holds significant importance due to the pivotal role of this compound as a gaseous messenger or gasotransmitter, intricately linked to the functions of the nervous and vascular systems, as well as inflammation. Specifically, CSE is associated with the production of this gasotransmitter in extraneural contexts, whereas CBS fulfills this role within the central nervous system (2). The enzyme facilitates the formation of H2S through a series of reactions classified into two main categories: cysteine-dependent beta reactions and homocysteine-dependent gamma reactions (3).
Structure
Cystathionine gamma-lyase exhibits a tetrameric quaternary structure when bound to its ligand (PLP), and in its apo form, it can exist as both a monomer and a tetramer, with the latter being more predominant [3]. The monomer comprises two domains: a .
The is characterized by the presence of an alpha/beta/alpha structure, and a mixed beta-sheet surrounded by eight alpha-helices. On the other hand, the possesses a four-stranded antiparallel beta-sheet and three alpha-helices on one side of the beta-sheet.
Disease
Structural highlights
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