Cofactors

There are no Cofactors for this Enzyme

Reaction Mechanism

uroporphyrinogen-III C-methyltransferase By Reference

The reference protein (CysG) covers three different domains/functions each component of which can be found as independent proteins in other organisms. This entry relates to the uroporphyrinogen-III C-methyltransferase function (residues 216-448 in the reference protein). This catalytic site catalyses two sequential methylation reactions using S-andenosyl-L-methionine (SAM), the first forming precorrin-1 and the second leading to the formation of precorrin-2. It is the first of three steps leading to the formation of siroheme from uroporphyrinogen III.




• Summary
• Step 1
• Step 2
• Step 3
• Step 4
• Step 5
• Step 6
• Products

The methyl transfers occur through SN2 type reactions in which the incoming methyl group undergoes stereochemical inversion. The nitrogen lone pair of ring A activates carbon C2 which subsequently performs nucleophilic attack on the methyl group bound to the sulfur of SAM. Asp248 carboxylate group abstracts a proton from the tetrapyrrole ring. Lys270 could serve as a general acid to promote tautomerization of the tetrapyrrole, facilitating proton abstraction by Asp248. The resultant rearrangement of double bonds (C1-NH+ and C3-C4 to C20-C1 and C4-C5 respectively) forms precorrin-1. The resultant S-adenosyl-L-homocystine (SAH) and precorrin-1 are lost from the active site followed by binding of new SAM and precorrin-1 in a new orientation placing C7 in the correct position for methylation. The above process is repeated at C7, forming a second SAH and precorrin-2.

Catalytic Residues

AA	Uniprot	Uniprot Resid	PDB	PDB Resid
Asp	P25924	248	1pjq	248
Lys	P25924	270	1pjq	270
Met	P25924	382	1pjq	382

Step Components

intermediate formation, native state of enzyme regenerated, overall reactant used, bimolecular nucleophilic substitution, tautomerisation (not keto-enol), proton transfer, overall product formed



Step 1.

A methyl group from SAM is added to C2 of the pyrrole ring in a biomolecular nucleophilic substitution reaction.



Step 2.

Asp 248 accepts a proton from the intermediate, causing tautomerization of the tetrapyrrole.



Step 3.

Further tautomerization of the enamine occurs and precorrin 1 is formed.



Step 4.

A methyl group is added to precorrin-1 by SAM in a bimolecular nucleophilic substitution reaction.



Step 5.

Asp248 deprotonates the intermediate. Subsequent rearrangement of the resulting enamine double bond forms precorrin 2.



Step 6.

In an inferred step Asp248 is deprotonated to regenerate the native state of the enzyme.



Products.

The products of the reaction.

View Reaction Mechanisms in M-CSA

Reaction Parameters

• Kinetic Parameters

  Organism	KM Value [mM]	Substrate	Comment
  Pseudomonas denitrificans (nom. rej.)	0.0063	S-adenosyl-L-methionine
  Desulfovibrio vulgaris	0.0004	uroporphyrinogen III	pH 8.0, 22°C, CobA/HemD
  Staphylococcus aureus	0.00124	uroporphyrinogen III	pH 8.0, temperature not specified in the publication
  Methanobacterium ivanovii	0.052	uroporphyrinogen III	pH 7.7, 30°C

• Temperature

  There are no reaction parameters information for this Enzyme.

• pH

  There are no reaction parameters information for this Enzyme.

Associated Proteins

Citations

• A synthetic cell-free 36-enzyme reaction system for vitamin B₁₂ production.
• Improved biosynthesis of heme in Bacillus subtilis through metabolic engineering assisted fed-batch fermentation.
• Identification of Photosynthesis Characteristics and Chlorophyll Metabolism in Leaves of Citrus Cultivar (Harumi) with Varying Degrees of Chlorosis.
• In Campylobacter jejuni, a new type of chaperone receives heme from ferrochelatase.
• Applications of the Whole-Cell System in the Efficient Biosynthesis of Heme.
• Pigment Biosynthesis and Molecular Genetics of Fruit Color in Pepper.
• Vitamin B₁₂ Auxotrophy in Isolates from the Deep Subsurface of the Iberian Pyrite Belt.
• Physiological and transcriptomic analysis of a yellow leaf mutant in watermelon.
• The Chemical Composition and Transcriptome Analysis Reveal the Mechanism of Color Formation in Tea (Camellia sinensis) Pericarp.
• Genome analysis of a coral-associated bacterial consortium highlights complementary hydrocarbon degradation ability and other beneficial mechanisms for the host.
• Structure of a closed-form uroporphyrinogen-III C-methyltransferase from Thermus thermophilus.