Structure and function study of the complex that synthesizesS-adenosylmethionine

Abstract

MAT2 complex is expressed in nearly all tissues and is essential in providing the necessary SAMe flux for methylation of DNA and various proteins including histones. X-ray crystallography and solution X-ray scattering structures of this complex show an unexpected stoichiometry, offering a unique mechanism of regulation and thus providing a gateway for structure-based drug design in anticancer therapies including liver disease.

Crystallography captures catalytic steps in human methionine adenosyltransferase enzymes

“…A diverse series of structures are available for MAT enzymes from bacteria, rat, and human (4,(10)(11)(12), which, supported by a range of biochemical evidence, have provided significant insight into the enzymatic mechanism. SAMe synthesis follows an SN 2 catalytic mechanism (13,14) in which the reaction is initiated through a nucleophilic attack by the sulfur atom of methionine on the C5′ atom of ATP, which produces the intermediate tripolyphosphate (PPPi).…”

“…The two ordered sites contain SAMe, PPNP, Mg 2+ , and K + , whereas the disordered sites contain only an ethylene glycol molecule as a result of the cryoprotection. The structure of (PPNP-bound) MATα2 has a disordered gating loop, and a comparison of the PPNP-bound, MAT(α2) 4 (βV2) 2 , and SAMe+ADO+MET+PPNP structures shows that the gate is open when active site is occupied by PPNP. In contrast, the gate is shut like a lid when the active site is occupied by SAMe or adenosine (Fig.…”

“…The structure of (PPNP-bound) MATα2 has a disordered gating loop, providing direct evidence against the idea that it provides the energy for the opening of the gate. The complex MAT(α2) 4 (βV2) 2 (PDB ID code 4NDN) contains four active sites, two that reveal ordered gating loops and two that do not show a gating loop, presumably owing to a highly flexible, disordered nature (4). The two ordered sites contain SAMe, PPNP, Mg 2+ , and K + , whereas the disordered sites contain only an ethylene glycol molecule as a result of the cryoprotection.…”

“…There are two major splicing forms of the MAT2B gene that encode for MATβV1 and MATβV2, which share very high sequence similarity and differ by only 20 residues in the N terminus (5). We recently reported that MATβ isoforms interact through their C terminus with MATα2 to form the MATαβ complexes MATαβV1 and MATαβV2 (4). MATα1 can exist in two oligomeric states, dimer and tetramer; however, there was little information on the oligomeric state of MATα2 until recently, when the structure of MATα2βV2 showed that MATα2 can exist and function as a tetramer in the presence of MATβ (4).…”

“…MAT2B encodes for MATβ, the regulatory subunit that has low sequence similarity (7%) to the catalytic subunits. MATα and MATβ subunits can form several MATαβ complexes (3,4). There are two major splicing forms of the MAT2B gene that encode for MATβV1 and MATβV2, which share very high sequence similarity and differ by only 20 residues in the N terminus (5).…”