Cofactors

Mg(2+).

Reaction Mechanism

holo-[acyl-carrier-protein] synthase By Reference

Holo-(acyl carrier protein) synthase (AcpS) from Bacillus subtilis is a member of the phosphopantetheinyl transferase superfamily. AcpS post-translationally modifies ACP to its holo form in order to activate it. AcpS catalyses the transfer of the 4'-phosphopantetheinyl (P-pant) moiety of coenzyme A to a serine residue on the ACP. This gives the activated ACP enzyme and Adenosine 3'5'-bisphosphate as products. This process is important as ACP enzymes play important roles in a number of biosynthetic pathways, such as the synthesis of fatty acids, vitamins, AcpS is essential in the initiation of the biosynthesis of fatty acids, polyketide antibiotics and non-ribosomal peptides.




• Summary
• Step 1
• Step 2
• Step 3
• Products

This enzyme requires either Mg(II) or Mn(II) for activity. The mechanism proceeds as follows: Asp 35 (in the substrate protein) deprotonates a water molecule. This activated water molecule then acts as a general base by deprotonating the substrate serine residue, activating it for nucleophilic attack on the beta-phosphate of CoA. The nucleophilic attack results in the transfer of the phosphopantetheinyl group to the substrate serine residue. The resulting negatively charged 3',5'-ADP is stabilised by interactions with Lys 62, the mainchain amide of His 105 and the magnesium ion. A proton is then transferred to 3',5'-ADP from either a water molecule or Lys 62.

Catalytic Residues

AA	Uniprot	Uniprot Resid	PDB	PDB Resid
His	P96618	105	1f80	104
Lys	P96618	62	1f80	61
Asp	P80643	36	1f80	40

Step Components

proton relay, intermediate formation, intermediate terminated, bimolecular nucleophilic addition, proton transfer, overall reactant used, unimolecular elimination by the conjugate base, intermediate collapse, overall product formed



Step 1.

Magnesium activated water deprotonates the Apo-ACP, activating it.



Step 2.

The activated Apo-ACP attacks the CoA in a nucleophilic addition, creating a pentavalent phosphate intermediate.



Step 3.

The pentavalent phosphate intermediate collapses, initiating an elimination of the adenosine 3',5'-bisphosphate product, which is reprotonated from a water molecule.



Products.

The products of the reaction.

View Reaction Mechanisms in M-CSA

Reaction Parameters

• Kinetic Parameters

  Organism	KM Value [mM]	Substrate	Comment
  Pseudomonas putida	3.3	CoA-[4'-phosphopantetheine]	in 100 mM Tris-HCl, pH 7.8, at 30°C
  Bacillus subtilis	3.5	CoA-[4'-phosphopantetheine]	in 100 mM Tris-HCl, pH 7.8, at 30°C
  Pseudomonas aeruginosa	20	CoA-[4'-phosphopantetheine]	in 100 mM Tris-HCl, pH 7.8, at 30°C

• Temperature

  There are no reaction parameters information for this Enzyme.

• pH

  Organism	pH Range	Comment
  Bacillus subtilis	4.5 - 8.5	less than 20% of maximum activity at both pH 5.0 and 7.0, 50% of activity maximum at pH 5.5 and pH 6.8
  Pseudomonas aeruginosa	5 - 7	pH 5: less than 27% of maximal activity, pH 7: less than 62% of maximal activity, activity with apo-[acyl-carrier protein]
  Escherichia coli	6 - 11	about 20% of activity maximum at pH 6.5, about 30% of activity maximum at pH 11.0
  Spinacia oleracea	7 - 8.8	half maximal activity at pH 7.4

Associated Proteins

Citations

• Structure, High Affinity, and Negative Cooperativity of the Escherichia coli Holo-(Acyl Carrier Protein):Holo-(Acyl Carrier Protein) Synthase Complex.
• Exploring the Chain Release Mechanism from an Atypical Apicomplexan Polyketide Synthase.
• Conformational Changes of Acyl Carrier Protein Switch the Chain Length Preference of Acyl-ACP Thioesterase ChFatB2.
• Enhancing the accumulation of lipid and docosahexaenoic acid in Schizochytrium sp. by co-overexpression of phosphopantetheinyl transferase and ω-3 fatty acid desaturase.
• In vitro characterization of nonribosomal peptide synthetase-dependent O-(2-hydrazineylideneacetyl)serine synthesis indicates a stepwise oxidation strategy to generate the α-diazo ester moiety of azaserine.
• Exploring the Chain Release Mechanism from an Atypical Apicomplexan Polyketide Synthase
• Structural advances toward understanding the catalytic activity and conformational dynamics of modular nonribosomal peptide synthetases.
• Herbicidal Active Compound Ferulic Acid Ethyl Ester Affects Fatty Acid Synthesis by Targeting the 3-Ketoacyl-Acyl Carrier Protein Synthase I (KAS I).
• Acyl carrier protein tag can enhance tobacco etch virus protease stability and promote its covalent immobilisation.
• Optimization of a hybrid bacterial/Arabidopsis thaliana fatty acid synthase system II in Saccharomyces cerevisiae.
• Incorporation and modification of fatty acids in cyanobacterial natural products biosynthesis.