D-Lysine 5,6-aminomutase

Chang, C. H., Frey, P. A. (2000) Cloning, sequencing, heterologous expression, purification, and characterization of adenosylcobalamin-dependent D-lysine 5,6-aminomutase from Clostridium sticklandii, J. Biol. Chem. 275, 106-114. 

Stereochemical Aspects The configuration of the product of the /Mysine 2,3-aminomutase reaction was established to be 3S,5S by NMR spectroscopic comparison of the d-lactam of the 3,5-diaminohexanoic acid 45 from C. sticklandii with authentic samples of both pairs of diastereomers [71]. The stereochemical mechanism of the / -lysine 5,6-aminomutase reaction was investigated by means of tritium labeling. It turned out that the pro-5 S hydrogen atom migrates to position 6 in the 3,5-diaminohexanoic acid [72] (Scheme 1.6.16). 

Besides a lysine 5,6-aminomutase, Clostridium sticklandii also has a D-ornithine 4,5-aminomutase (EC 5.4.3.5) [78, 79], D-Ornithine is generated from L-ornithine by ornithine racemase [80], The two genes encoding D-ornithine 4,5-aminomutase have been cloned, sequenced, and expressed in E. coli [81]. The enzyme is an a2/ 2-heterotetramer, consisting of 12 800 Da and 82 900 Da subunits. The protein requires Bn and pyridoxal phosphate as cofactors. Similar to the lysine 5,6-aminomutase, a conserved base-ofi)/histidine-on cobalamin binding motif is present in the 82 900 Da protein. 

P-Lysine aminomutase has also been shown to catalyze the transformation of D-lysine into D-2,5-diaminohexanoate, and the enzyme has been described as o/p-lysine 5,6-aminomutase (o/P-LAM). ... 

FIGURE 4. The eleven adenosylcobalamin-dependent rearrangements so far described. Notes D-a-lysine [L-p-lysine] 5,6-aminomutase catalyzes similar rearrangements on two substrates diol dehydrase and glycerol dehydrase have over-lapping substrate specificity. 

Lysine 5,6-aminomutase (5,6-LAM) catalyzes the isomerization of D-lysine to 2,5-diaminohexanoic acid [180,181]. The mechanism proposed is analogous to that of D-ornithine amino mutase [228,229]. 5,6-LAM was predicted to be a base-off/His-on Bi2-dependent enzyme [230], as was recently conformed by the crystal structure [231]. 

Reaction Mechanism Although the /Mysine 5,6-aminomutase requires cobalamin as cofactor instead of SAM its reaction mechanism seems to be similar to that of the lysine 2,3-aminomutase [73], Experiments with tritium-labeled lysine and B12 showed that Bn is directly involved in the hydrogen shift from position 5 in d-... 

Aminomutases. The enzymes L-p-lysine mutase (which is also D-a-lysine mutase) and D-omithine mutase catalyze the transfer of an co-amino group to an adjacent carbon atom (Table 16-1). Two proteins are needed for the reaction pyridoxal phosphate is required and is apparently directly involved in the amino group migration. In the P-lysine mutase the 6-amino group of L-P-lysine replaces the pro-S hydrogen at C-5 but with inversion at C-5 to yield (3S, 5S)-... 

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