PDBsum entry 1gli

Oxygen transport

PDB id: 1gli

Contents

Protein chains

141 a.a. *

146 a.a. *

Ligands

HEM ×4

PO4

Waters ×110

* Residue conservation analysis

References listed in PDB file

Key reference

• Title: Probing the alpha 1 beta 2 interface of human hemoglobin by mutagenesis. Role of the fg-C contact regions.
• Authors: B.Vallone, A.Bellelli, A.E.Miele, M.Brunori, G.Fermi.
• Ref.: J Biol Chem, 1996, 271, 12472-12480.
• PubMed id: 8647854

Note In the PDB file this reference is annotated as "TO BE PUBLISHED". The citation details given above were identified by an automated search of PubMed on title and author names, giving a percentage match of 83%.

Abstract

The allosteric transition of hemoglobin involves an extensive reorganization of the alpha 1 beta 2 interface, in which two contact regions have been identified. This paper concerns at the effect of two mutations located in the "switch" (alpha C3 Thr --> Trp) and the "flexible joint" (beta C3 Trp --> Thr). We have expressed and characterized one double and two single mutants: Hb alpha T38W/beta W37T, Hb beta W37T, and Hb alpha T38W, whose structure has been determined by crystallography. We present data on: (i) the interface structure in the contact regions, (ii) oxygen and CO binding kinetics and cooperativity, (iii) dissociation rates of deoxy tetramers and association rates of deoxy dimers, and (iv) the effect of NaI on deoxy tetramer dissociation rate constant. All the mutants are tetrameric and T-state in the deoxygenated derivative. Reassociation of deoxygenated dimers is not modified by interface mutations. DeoxyHb alpha T38W/beta W37T dissociate much faster. We propose a binding site for I- at the switch region. The single mutants binds O2 cooperatively; the double one is almost non-cooperative, a feature confirmed by CO binding. The functional data, analyzed with the two-state model, indicate that these mutations reduce the value of the allosteric constant LO.