{PDOC51014}
{PS51014; COBK_CBIJ}
{BEGIN}
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* Precorrin-6x reductase domain profile *
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Cobalamins (vitamin  B12), both as deoxyadenosylcobalamin and methylcobalamin,
are involved  as  cofactors  in  a  variety  of  enzymatic  reactions  and are
synthesized by some bacteria and archaea. About thirty enzymes are required to
manufacture cobalamins,  some  of  the  most  complex  nonpolymeric  molecules
biosynthesized in  the  cell. Cobalamin biosynthesis can be divided into three
distinct sections.  The  first  results  in  the  synthesis of the corrin ring
component, cobinamide,   from   the   ubiquitous   tetrapyrrole   primogenitor
uroporphyrinogen III  by  a  series of reactions including eight S-adenosyl-L-
methionine-dependent methylations,   ring   contraction,   cobalt   chelation,
decarboxylation, amidations,  and  1-amino-2-propanol  attachment.  The second
results in  the  synthesis  of  the  lower axial ligand, dimethylbenzimidazole
(DMB) and  the  third  results  in the assembly of the final coenzyme from the
attachment of  the corrin ring to the DMB as well as the addition of the upper
coordinating ligand for the cobalt, either an adenosyl or a methyl group [1].

The precorrin-6x reductase (EC 1.3.1.54) domain is found in proteins (cobK and
cbiJ), which  are involved in part I of the cobalamin biosynthesis pathway. It
catalyzes the  NADPH-dependent    reduction    of    precorrin-6x to a dihydro
derivative named precorrin-6y [2,3].

The profile we developed covers the entire precorrin-6x reductase domain.

-Sequences known to belong to this class detected by the profile: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: August 2004 / First entry.

[ 1] Raux E., Schubert H.L., Warren M.J.
     "Biosynthesis of cobalamin (vitamin B12): a bacterial conundrum."
     Cell. Mol. Life Sci. 57:1880-1893(2000).
     PubMed=11215515
[ 2] Blanche F., Thibaut D., Famechon A., Debussche L., Cameron B.,
     Crouzet J.
     "Precorrin-6x reductase from Pseudomonas denitrificans: purification
     and characterization of the enzyme and identification of the
     structural gene."
     J. Bacteriol. 174:1036-1042(1992).
     PubMed=1732193
[ 3] Shearer N., Hinsley A.P., Van Spanning R.J.M., Spiro S.
     "Anaerobic growth of Paracoccus denitrificans requires cobalamin:
     characterization of cobK and cobJ genes."
     J. Bacteriol. 181:6907-6913(1999).
     PubMed=10559155

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