Crystal structure of human T-protein of glycine cleavage system at 2.0 A resolution and its implication for understanding non-ketotic hyperglycinemia.

摘要: T-protein, a component of the glycine cleavage system, catalyzes formation ammonia and 5,10-methylenetetrahydrofolate from aminomethyl moiety attached to lipoate cofactor H-protein. Several mutations in human T-protein gene cause non-ketotic hyperglycinemia. To gain insights into effect disease-causing catalytic mechanism at molecular level, crystal structures free form that bound 5-methyltetrahydrofolate (5-CH 3 -H 4 folate) have been determined 2.0 A 2.6 A resolution, respectively. The overall structure consists three domains arranged cloverleaf-like with central cavity, where 5-CH folate is kinked shape pteridine group deeply buried hydrophobic pocket glutamyl pointed C-terminal side surface. Most disease-related residues cluster around forming extensive hydrogen bonding networks. These networks are employed holding not only folate-binding space but also positions orientations α-helix G following loop middle region, which seems play pivotal role catalysis. Structural mutational analyses demonstrated Arg292 interacts through water molecules polyglutamate tail, invariant Asp101, located close N10 folate, might key initiation catalysis by increasing nucleophilic character atom substrate for attack on intermediate. A clever recruiting arm reaction site function as way avoiding release toxic formaldehyde.