Methionine synthase crystal structure

The first coenzyme Bi2-dependent isomerase to be crystallized and structurally analyzed by X-ray crystallography is MCM. Several crystal structures of MCM are available, and one is illustrated in Figure 23. Like GM and 5,6-LAM, the larger subunit is a TIM barrel. Also like GM, MCM, and methionine synthase, adenosylcobalamin is bound in a base-ofF mode. 

Wolthers KR, Lou X, Toogood HS, Leys D, Scrutton NS (2007) Mechanism of coenzyme binding to human methionine synthase reductase revealed through the crystal structure of the FNR-like module and isothermal titration calorimetry. Biochemistry 46 11833-11844... 

Then the 7,8-diaminononanoate (7,8-diaminopelargonic acid) (Scheme 12.93) is converted to the bisamide dethiobiotin (an imidazolidone) by carboxylation with carbon dioxide (CO2) in the presence of ATP in a reaction requiring magnesium (Mg+ ) and catalyzed by dethiobiotin synthase (EC 6.3.3.3). The well-known reversible reaction of amines with carbon dioxide (CO2) and an X-ray crystal structure showing the 8-amino group as a mixed carbonic phosphate anhydride has lent support to this picture (PDB la82). Finally, in the presence of biotin synthase (EC 2.8.1.6), an enzyme that appears to be used only once in each synthesis, reaction occurs with 2 equivalents (but almost certainly one at a time) of SAM and sulfur to produce biotin, 2 equivalents of methionine (Met, M), and 2 equivalents of 5 -deoxyadenosine. 

---