PDBsum entry 1hk5

Plasma protein

PDB id: 1hk5

Contents

Protein chain

582 a.a. *

Ligands

MYR ×7

T44

Waters ×18

* Residue conservation analysis

PDB id:

1hk5

Name:

Plasma protein

Title:

Human serum albumin mutant r218h complexed with thyroxine (3,3',5,5'- tetraiodo-l-thyronine) and myristic acid (tetradecanoic acid)

Structure:

Serum albumin. Chain: a. Engineered: yes. Mutation: yes

Source:

Homo sapiens. Human. Organism_taxid: 9606. Expressed in: pichia pastoris. Expression_system_taxid: 4922

Resolution:

2.70Å R-factor: 0.199 R-free: 0.259

Authors:

I.Petitpas,C.E.Petersen,C.E.Ha,A.A.Bhattacharya,P.A.Zunszain, J.Ghuman,N.V.Bhagavan,S.Curry

Key ref:

I.Petitpas et al. (2003). Structural basis of albumin-thyroxine interactions and familial dysalbuminemic hyperthyroxinemia. Proc Natl Acad Sci U S A, 100, 6440-6445. PubMed id: 12743361 DOI: 10.1073/pnas.1137188100

Date:

05-Mar-03 Release date: 16-May-03

Protein chain

P02768  (ALBU_HUMAN) -  Albumin from Homo sapiens

Seq: 609 a.a.

Struc: 582 a.a.*

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

DOI no: 10.1073/pnas.1137188100

Proc Natl Acad Sci U S A 100:6440-6445 (2003)

PubMed id: 12743361

Structural basis of albumin-thyroxine interactions and familial dysalbuminemic hyperthyroxinemia.

I.Petitpas, C.E.Petersen, C.E.Ha, A.A.Bhattacharya, P.A.Zunszain, J.Ghuman, N.V.Bhagavan, S.Curry.

ABSTRACT

Human serum albumin (HSA) is the major protein component of blood plasma and serves as a transporter for thyroxine and other hydrophobic compounds such as fatty acids and bilirubin. We report here a structural characterization of HSA-thyroxine interactions. Using crystallographic analyses we have identified four binding sites for thyroxine on HSA distributed in subdomains IIA, IIIA, and IIIB. Mutation of residue R218 within subdomain IIA greatly enhances the affinity for thyroxine and causes the elevated serum thyroxine levels associated with familial dysalbuminemic hyperthyroxinemia (FDH). Structural analysis of two FDH mutants of HSA (R218H and R218P) shows that this effect arises because substitution of R218, which contacts the hormone bound in subdomain IIA, produces localized conformational changes to relax steric restrictions on thyroxine binding at this site. We have also found that, although fatty acid binding competes with thyroxine at all four sites, it induces conformational changes that create a fifth hormone-binding site in the cleft between domains I and III, at least 9 A from R218. These structural observations are consistent with binding data showing that HSA retains a high-affinity site for thyroxine in the presence of excess fatty acid that is insensitive to FDH mutations.

Selected figure(s)

Figure 1.
Fig. 1. Comparison of the structures of HSA-T[4] and (a) HSA-myristate-T[4] (b). The protein secondary structure is shown schematically with the subdomains color-coded as follows: IA, red; IB, light red; IIA, green; IIB, light-green; IIIA, blue; IIIB, light blue. This color scheme is maintained throughout. Ligands are shown in a space-filling representation, colored by atom type: carbon (fatty acid), gray; carbon (T[4]), brown; nitrogen, blue; oxygen, red; iodine, magenta. T[4]-binding sites are labeled Tr1-Tr5; fatty acid-binding sites are labeled FA1-FA7. Except where stated otherwise, molecular graphics were prepared by using BOBSCRIPT (40) and RASTER3D (41). (c)An F[obs] - F[calc] simulated annealing omit map (29) contoured at 3 for T[4] bound to site Tr1 in subdomain IIA of the R218P mutant. Selected amino acid side chains are colored by atom type. Hydrogen bonds are indicated by dashed orange lines. (d) Schematic structure of T[4] hormone, indicating key nomenclature.

Figure 2.
Fig. 2. Comparison of the bound configurations of T[4] in HSA. (a) Site Tr1 in subdomain IIA. There is only very weak electron density for the side chain of R218 because variation in the position of this residue and atoms beyond C were omitted from the refined model; the position shown in the figure is indicative only but is consistent with the location of the main-chain atoms and steric constraints imposed by neighboring residues and the T[4] ligand. (b) Site Tr2 in subdomain IIIA. (c) Sites Tr3 and Tr4 in subdomain IIIB (from the R218H mutant structure, because this model shows the least disorder of the C-terminal helix). (d) Site Tr5 in the interdomain cleft of the HSA-myristate complex. Figures were prepared by using MOLSCRIPT (41) and PYMOL (42). Selected amino acid side chains are shown colored by atom type. The van der Waals surface of the ligand is represented by a semitransparent magenta surface. Hydrogen bonds are indicated by dashed orange lines.

Figures were selected by the author.