Oxyanion hole explained

An oxyanion hole is a pocket in the active site of an enzyme that stabilizes transition state negative charge on a deprotonated oxygen or alkoxide.^[1] The pocket typically consists of backbone amides or positively charged residues. Stabilising the transition state lowers the activation energy necessary for the reaction, and so promotes catalysis.^[2] For example, proteases such as chymotrypsin contain an oxyanion hole to stabilise the tetrahedral intermediate anion formed during proteolysis and protects substrate's negatively charged oxygen from water molecules.^[3] Additionally, it may allow for insertion or positioning of a substrate, which would suffer from steric hindrance if it could not occupy the hole (such as BPG in hemoglobin). Enzymes that catalyse multi-step reactions can have multiple oxyanion holes that stabilise different transition states in the reaction.^[4]

See also

• Enzyme catalysis
• Active site
• Transition state
• Serine proteases#Catalytic mechanism

References

• Book: Albert Lehninger. Albert Lehninger. Principles of Biochemistry. 2008. 5th. Macmillan. 207. 9780716771081. etal.

Notes and References

1. Book: Stryer L, Berg JM, Tymoczko JL . Biochemistry. W.H. Freeman. San Francisco. 2002. 5th. 978-0-7167-4955-4. 9 Catalytic Strategies. https://www.ncbi.nlm.nih.gov/books/NBK22526/.
2. Enzyme Catalysis by Hydrogen Bonds: The Balance between Transition State Binding and Substrate Binding in Oxyanion Holes. The Journal of Organic Chemistry. March 19, 2010. 0022-3263. 1831–1840. 75. 6. 10.1021/jo901503d. Luis. Simón. Jonathan M.. Goodman. 20039621.
3. Oxyanion Hole Interactions in Serine and Cysteine Proteases. Biological Chemistry Hoppe-Seyler. 373. 2. 393–400. 10.1515/bchm3.1992.373.2.393. 1992. Ménard. Robert. Storer. Andrew C.. 1387535.
4. The Catalytic Cycle of Biosynthetic Thiolase: A Conformational Journey of an Acetyl Group through Four Binding Modes and Two Oxyanion Holes‡. Biochemistry. December 1, 2002. 0006-2960. 15543–15556. 41. 52. 10.1021/bi0266232. Petri. Kursula. Juha. Ojala. Anne-Marie. Lambeir. Rik K.. Wierenga. 12501183.