The crystal structure of coenzyme B 12 ‐dependent glycerol dehydratase in complex with cobalamin and propane‐1,2‐diol
Recombinant glycerol dehydratase of Klebsiella pneumoniae was purified to homogeneity. The subunit composition of the enzyme was most probably α 2 β 2 γ 2 . When ( R )‐ and ( S )‐propane‐1,2‐diols were used independently as substrates, the rate with the ( R )‐enantiomer was 2.5 times faster than tha...
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Published in | European journal of biochemistry Vol. 269; no. 18; pp. 4484 - 4494 |
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Main Authors | , , , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
01.09.2002
|
Online Access | Get full text |
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Summary: | Recombinant glycerol dehydratase of
Klebsiella pneumoniae
was purified to homogeneity. The subunit composition of the enzyme was most probably α
2
β
2
γ
2
. When (
R
)‐ and (
S
)‐propane‐1,2‐diols were used independently as substrates, the rate with the (
R
)‐enantiomer was 2.5 times faster than that with the (
S
)‐isomer. In contrast to diol dehydratase, an isofunctional enzyme, the affinity of the enzyme for the (
S
)‐isomer was essentially the same or only slightly higher than that for the (
R
)‐isomer (
K
m(
R
)
/
K
m(
S
)
= 1.5). The crystal structure of glycerol dehydratase in complex with cyanocobalamin and propane‐1,2‐diol was determined at 2.1 Å resolution. The enzyme exists as a dimer of the αβγ heterotrimer. Cobalamin is bound at the interface between the α and β subunits in the so‐called ‘base‐on’ mode with 5,6‐dimethylbenzimidazole of the nucleotide moiety coordinating to the cobalt atom. The electron density of the cyano group was almost unobservable, suggesting that the cyanocobalamin was reduced to cob(II)alamin by X‐ray irradiation. The active site is in a (β/α)
8
barrel that was formed by a central region of the α subunit. The substrate propane‐1,2‐diol and essential cofactor K
+
are bound inside the (β/α)
8
barrel above the corrin ring of cobalamin. K
+
is hepta‐coordinated by the two hydroxyls of the substrate and five oxygen atoms from the active‐site residues. These structural features are quite similar to those of diol dehydratase. A closer contact between the α and β subunits in glycerol dehydratase may be reminiscent of the higher affinity of the enzyme for adenosylcobalamin than that of diol dehydratase. Although racemic propane‐1,2‐diol was used for crystallization, the substrate bound to glycerol dehydratase was assigned to the (
R
)‐isomer. This is in clear contrast to diol dehydratase and accounts for the difference between the two enzymes in the susceptibility of suicide inactivation by glycerol. |
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ISSN: | 0014-2956 1432-1033 |
DOI: | 10.1046/j.1432-1033.2002.03151.x |