1BBB

A THIRD QUATERNARY STRUCTURE OF HUMAN HEMOGLOBIN A AT 1.7-ANGSTROMS RESOLUTION

DOI: 10.2210/pdb1BBB/pdb

Classification: OXYGEN TRANSPORT
Organism(s): Homo sapiens
Mutation(s): No

Deposited: 1992-04-29 Released: 1993-10-31
Deposition Author(s): Arnone, A., Silva, M.M.

Experimental Data Snapshot

Method: X-RAY DIFFRACTION
Resolution: 1.70 Å
R-Value Observed: 0.184

wwPDB Validation3D Report Full Report

This is version 1.2 of the entry. See complete history.

Literature

A third quaternary structure of human hemoglobin A at 1.7-A resolution.

Silva, M.M., Rogers, P.H., Arnone, A.

(1992) J Biol Chem 267: 17248-17256

PubMed: 1512262 Search on PubMed
Primary Citation of Related Structures:
1BBB

PubMed Abstract:

Previous crystallographic studies have shown that human hemoglobin A can adopt two stable quaternary structures, one for deoxyhemoglobin (the T-state) and one for liganded hemoglobin (the R-state). In this paper we report our finding of a second quaternary structure (the R2-state) for liganded hemoglobin A. The magnitudes of the spatial differences between the R- and R2-states are as large as those between the R- and T-states. Of particular interest are the structural changes that occur as a result of R-T and R-R2 transitions at the so-called "switch" region of the critical alpha 1 beta 2 interface. In the R-state, His-97 beta 2 is positioned between Thr-38 alpha 1 and Thr-41 alpha 1, whereas in transition to the T-state His 97 beta 2 must "jump" a turn in the alpha 1 C helix to form nonpolar contacts with Thr-41 alpha 1 and Pro-44 alpha 1. This facet of the R-T transition presents a major steric barrier to the quaternary structure change. In the R2-state, His-97 beta 2 simply rotates away from threonines 38 alpha 1 and 41 alpha 1, breaking contact with these residues and allowing water access to the center of the alpha 1 beta 2 interface. With the switch region in an open position in the R2-state, His-97 beta 2 should be able to move by Thr-41 alpha 1 and make the transition to the T-state with a steric barrier that is less than that for the R-T transition. Thus the R2-state may function as a stable intermediate along a R-R2-T pathway. The T-, R-, and R2-states must coexist in solution. That is, the fact that these states can be crystallized implies that they are all energetically accessible structures. What remains to be determined are the T-to-R, T-to-R2, and R-to-R2 equilibrium constants for hemoglobin under various solution conditions and ligation states. Although this may prove to be difficult, we discuss previously published results which indicate that low concentrations of inorganic anions or low pH may favor the R2-state and at least one alpha 1 beta 2 interface mutation stabilizes a quaternary structure that is very similar to the R2-state.

Organizational Affiliation:

Department of Biochemistry, University of Iowa, Iowa City 52242.

Macromolecules

Find similar proteins by:

(by identity cutoff) | Structure

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
HEMOGLOBIN A (CARBONMONOXY) (ALPHA CHAIN)	A, C	141	Homo sapiens	Mutation(s): 0 Gene Names: HBA1, HBA2
Find proteins for P69905 (Homo sapiens) Explore P69905 Go to UniProtKB: P69905
NIH Common Fund Data Resources
PHAROS P69905 GTEx ENSG00000188536GTEx ENSG00000206172
Protein Feature View Expand
( Mouse scroll to zoom / Hold left click to move ) Reference Sequence

Find similar proteins by:

(by identity cutoff) | Structure

Entity ID: 2
Molecule	Chains	Sequence Length	Organism	Details	Image
HEMOGLOBIN A (CARBONMONOXY) (BETA CHAIN)	B, D	146	Homo sapiens	Mutation(s): 0 Gene Names: HBB
Find proteins for P68871 (Homo sapiens) Explore P68871 Go to UniProtKB: P68871
NIH Common Fund Data Resources
PHAROS P68871 GTEx ENSG00000244734
Protein Feature View Expand
( Mouse scroll to zoom / Hold left click to move ) Reference Sequence

Small Molecules

Ligands 2 Unique
ID	Chains	Name / Formula / InChI Key	2D Diagram	3D Interactions
HEM Query on HEM Download CCD File	A, B, C, D	PROTOPORPHYRIN IX CONTAINING FE C₃₄ H₃₂ Fe N₄ O₄ KABFMIBPWCXCRK-RGGAHWMASA-L		Ligand Interaction
CMO Query on CMO Download CCD File	A, B, C, D	CARBON MONOXIDE C O UGFAIRIUMAVXCW-UHFFFAOYSA-N		Ligand Interaction