PDBsum entry 2hz3

Oxygen storage/transport

PDB id: 2hz3

Contents

Protein chain

123 a.a. *

Ligands

SO2 ×2

HEM

Metals

_CD ×2

Waters ×81

* Residue conservation analysis

PDB id:

2hz3

Name:

Oxygen storage/transport

Title:

The x-ray crystal structure of ferrous synechocystis hemoglobin h117a mutant with a covalent linkage

Structure:

Cyanoglobin. Chain: a. Synonym: hemoglobin, hb. Engineered: yes. Mutation: yes

Source:

Synechocystis sp.. Organism_taxid: 1148. Strain: pcc 6803. Gene: glbn. Expressed in: escherichia coli. Expression_system_taxid: 562

Resolution:

1.90Å R-factor: 0.196 R-free: 0.240

Authors:

J.A.Hoy

Key ref:

J.A.Hoy et al. (2007). Covalent heme attachment in Synechocystis hemoglobin is required to prevent ferrous heme dissociation. Protein Sci, 16, 250-260. PubMed id: 17242429 DOI: 10.1110/ps.062572607

Date:

08-Aug-06 Release date: 29-Aug-06

Protein chain

P73925  (TRHBN_SYNY3) -  Group 1 truncated hemoglobin GlbN from Synechocystis sp. (strain PCC 6803 / Kazusa)

Seq: 124 a.a.

Struc: 123 a.a.*

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

Enzyme reactions

• Enzyme class: E.C.?

DOI no: 10.1110/ps.062572607

Protein Sci 16:250-260 (2007)

PubMed id: 17242429

Covalent heme attachment in Synechocystis hemoglobin is required to prevent ferrous heme dissociation.

J.A.Hoy, B.J.Smagghe, P.Halder, M.S.Hargrove.

ABSTRACT

Synechocystis hemoglobin contains an unprecedented covalent bond between a nonaxial histidine side chain (H117) and the heme 2-vinyl. This bond has been previously shown to stabilize the ferric protein against denaturation, and also to affect the kinetics of cyanide association. However, it is unclear why Synechocystis hemoglobin would require the additional degree of stabilization accompanying the His117-heme 2-vinyl bond because it also displays endogenous bis-histidyl axial heme coordination, which should greatly assist heme retention. Furthermore, the mechanism by which the His117-heme 2-vinyl bond affects ligand binding has not been reported, nor has any investigation of the role of this bond on the structure and function of the protein in the ferrous oxidation state. Here we report an investigation of the role of the Synechocystis hemoglobin His117-heme 2-vinyl bond on structure, heme coordination, exogenous ligand binding, and stability in both the ferrous and ferric oxidation states. Our results reveal that hexacoordinate Synechocystis hemoglobin lacking this bond is less stable in the ferrous oxidation state than the ferric, which is surprising in light of our understanding of pentacoordinate Hb stability, in which the ferric protein is always less stable. It is also demonstrated that removal of the His117-heme 2-vinyl bond increases the affinity constant for intramolecular histidine coordination in the ferric oxidation state, thus presenting greater competition for the ligand binding site and lowering the observed rate and affinity constants for exogenous ligands.

Selected figure(s)

Figure 1.
Figure 1. SynHb (gray) versus SynH117A (colored by RMSD from SynHb,

Figure 2.
Figure 2. Rapid mixing kinetic measurement of CO binding. (A) Change

The above figures are reprinted by permission from the Protein Society: Protein Sci (2007, 16, 250-260) copyright 2007.

Figures were selected by an automated process.