Poly(A) Polymerase

From Proteopedia

Revision as of 12:47, 27 February 2013

Poly(A) Polymerase (polynucleotide adenylytransferase, EC 2.7.7.19) is the enzyme responsible for adding a polyadenine tail to the 3' end of a nascent pre-mRNA transcript. Its substrates are ATP and RNA. The poly(A) tail that poly-A polymerase adds to the 3' end of the pre-mRNA transcript is important for nuclear export, translation and stability of the mRNA.

Determinants of ATP Recognition

spinqualitylabelsall models Structure of Yeast Poly(A) Polymerase with ATP and oligo(A) (PDB entry 2q66) Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image Poly(A) Polymerase binds specifically to ATP and adds it the end of a messenger RNA chain. This structure contains an oligo(A) polynucleotide with five nucleotides, an ATP molecule, and a magnesium ion. The enzyme is an inactive mutant with the catalytic aspartate 154 changed to alanine. Poly(A) polymerase normally has a second magnesium ion, but that second magnesium ion is absent from this structure due to the inactivating mutation D154A. In the , the enzyme is in blue backbone representation, the RNA chain is in yellow, the ATP is in red, the magnesium is in green, and ALA154 is in magenta. Several mechanisms are used to achieve the specificity for ATP. The magnesium is coordinated by , and the magnesium coordinates with the phosphates of ATP, positioning the nucleotide in the active site. The adenine base is sandwiched between the . Surprisingly, there are very few contacts with the hydrogen-bonding groups in the adenine base. may form a hydrogen bond to adenine in the active enzyme, but the distance is a bit too long in this mutant structure. Instead of forming specific hydrogen bonds with the enzyme, most of the hydrogen-bonding groups in the base, sugar and phosphate interact with a shell of . Discrimination between ATP and GTP is achieved through a close steric contact between the . Guanine bases have an extra amino group at this position that would be too bulky to fit against these amino acids.

This section complements the article on Poly(A) Polymerase in the Molecule of the Month Series. See also Teaching Scenes, Tutorials, and Educators' Pages.

3D structures of poly(A) polymerase

3aqk, 3aql, 3aqm, 3aqn – PAP residues 18-431 – Escherichia coli
1jsz - VvPAP regulatory subunit residues 1-307 – Vaccinia virus
1jte, 1eam - VvPAP regulatory subunit residues 1-307 (mutant)
2hhp, 2o1p – yPAP - yeast
1q79, 1f5a - bPAP-α - bovine

Poly(A) polymerase complex

3er8, 3er9, 3erc – VvPAP catalytic subunit + RNA
2ga9 - VvPAP catalytic subunit + CAP-specific mRNA methyltransferase + ATP
2gaf - VvPAP catalytic subunit (mutant) + CAP-specific mRNA methyltransferase
1jtf, 2vp3 - VvPAP regulatory subunit residues 1-307 (mutant) + M7GPPPG
1b42, 1bky, 1eqa, 3mag, 3mct, 4dcg, 1av6, 1p39, 1v39 - VvPAP regulatory subunit residues 1-297 (mutant) + purine derivative + adenosylhomocysteine
1vp3 - VvPAP regulatory subunit + adenosylhomocysteine
1vp9 - VvPAP regulatory subunit (mutant) + adenosylhomocysteine
1vpt - VvPAP regulatory subunit (mutant) + adenosylmethionine
3c66 - yPAP residues 1-526 + Fip1 peptide
2q66 – yPAP + polyA + ATP
1q78 – bPAP-α + Mg + ATP

Additional Resources

For additional information, see: Translation
For additional examples of transferases, see: Transferase

• PDB entry 2q66

Reference

Mechanism of poly(A) polymerase: structure of the enzyme-MgATP-RNA ternary complex and kinetic analysis., Balbo PB, Bohm A, Structure. 2007 Sep;15(9):1117-31. PMID:17850751