Subunit association as the stabilizing determinant for archaeal methionine adenosyltransferases

摘要: Archaea contain a class of methionine adenosyltransferases (MATs) that exhibit substantially higher stability than their mesophilic counterparts. Their sequences are highly divergent, but preserve the essential active site motifs family. We have investigated origin this increased using chemical denaturation experiments on Methanococcus jannaschii MAT (Mj-MAT) and mutants containing single tryptophans in place tyrosine residues. The results from fluorescence, circular dichroism, hydrodynamic, enzyme activity measurements showed Mj-MAT derives largely tighter association its subunits dimer. Local fluorescence changes, interpreted secondary structure predictions, further identify least stable structural elements as C-terminal ends β-strands E2 E6, N-terminus E3. Dimer dissociation however requires wider perturbation molecule. Additional analysis was initially hindered by lack crystal structures for archaeal MATs, limitation we overcame construction 3D-homology model Mj-MAT. This predicts preservation chain topology three-domain organization typical family, locates at flat contact surface between monomers, shows alterations all three domains required dimer dissociation.