PDBsum entry 3mnh

Proton transport

PDB id: 3mnh

Contents

Protein chain

258 a.a. *

Metals

_NA

_ZN

Waters ×136

* Residue conservation analysis

PDB id:

3mnh

Name:

Proton transport

Title:

Human carbonic anhydrase ii mutant k170a

Structure:

Carbonic anhydrase 2. Chain: a. Synonym: carbonic anhydrase ii, ca-ii, carbonate dehydratase ii, carbonic anhydrasE C, cac. Engineered: yes. Mutation: yes

Source:

Homo sapiens. Human. Organism_taxid: 9606. Gene: ca2. Expressed in: escherichia coli. Expression_system_taxid: 562.

Resolution:

1.65Å R-factor: 0.156 R-free: 0.188

Authors:

J.F.Domsic,R.Mckenna

Key ref:

J.F.Domsic et al. (2010). Structural and kinetic study of the extended active site for proton transfer in human carbonic anhydrase II. Biochemistry, 49, 6394-6399. PubMed id: 20578724

Date:

21-Apr-10 Release date: 14-Jul-10

Protein chain

P00918  (CAH2_HUMAN) -  Carbonic anhydrase 2 from Homo sapiens

Seq: 260 a.a.

Struc: 258 a.a.*

* PDB and UniProt seqs differ at 1 residue position (black cross)

Enzyme reactions

• Enzyme class: E.C.4.2.1.1 - carbonic anhydrase.
• Reaction: hydrogencarbonate + H⁺ = CO2 + H2O
• Cofactor: Zn(2+)

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

Added reference

Biochemistry 49:6394-6399 (2010)

PubMed id: 20578724

Structural and kinetic study of the extended active site for proton transfer in human carbonic anhydrase II.

J.F.Domsic, W.Williams, S.Z.Fisher, C.Tu, M.Agbandje-McKenna, D.N.Silverman, R.McKenna.

ABSTRACT

The catalysis of CO(2) hydration by human carbonic anhydrase II (HCA II) is limited in maximal velocity by proton transfer from a zinc-bound water molecule to the proton shuttle His64. This proton transfer occurs along a hydrogen-bonded water network, leading to the proton shuttle residue His64, which in turn transfers the proton to bulk solvent. The side chain of His64 occupies two conformations in wild-type HCA II, pointing inward toward the zinc or outward toward bulk solvent. Previously, several studies have examined the roles of residues of the active site cavity that interact with the solvent-mediated hydrogen-bonded network between His64 and the zinc-bound water. Here these studies are extended to examine the effects on proton transfer by mutation at Lys170 (to Ala, Asp, Glu, and His), a residue located near the side chain of His64 but over 15 A away from the active site zinc. In all four variants, His64 is observed in the inward conformation associated with a decrease in the pK(a) of His64 by as much as 1.0 unit and an increase in the rate constant for proton transfer to as much as 4 micros(-1), approximately 5-fold larger than wild-type HCA II. The results show a significant extension of the effective active site of HCA II from the zinc-bound water at the base of the conical cavity in the enzyme to Lys170 near the rim of the cavity. These data emphasize that the active site of HCA II is extended to include residues that, at first glance, appear to be too far from the zinc to exert any catalytic effects.