Interdomain zinc site on human albumin

Proc Natl Acad Sci U S A. 2003 Apr 1;100(7):3701-6. doi: 10.1073/pnas.0436576100. Epub 2003 Feb 21.

Abstract

Albumin is the major transport protein in blood for Zn(2+), a metal ion required for physiological processes and recruited by various drugs and toxins. However, the Zn(2+)-binding site(s) on albumin is ill-defined. We have analyzed the 18 x-ray crystal structures of human albumin in the PDB and identified a potential five-coordinate Zn site at the interface of domains I and II consisting of N ligands from His-67 and His-247 and O ligands from Asn-99, Asp-249, and H(2)O, which are the same amino acid ligands as those in the zinc enzymes calcineurin, endonucleotidase, and purple acid phosphatase. The site is preformed in unliganded apo-albumin and highly conserved in mammalian albumins. We have used (111)Cd NMR as a probe for Zn(2+) binding to recombinant human albumin. We show that His-67 --> Ala (His67Ala) mutation strongly perturbs Cd(2+) binding, whereas the mutations Cys34Ala, or His39Leu and Tyr84Phe (residues which may H-bond to Cys-34) have no effect. Weak Cl(-) binding to the fifth coordination site of Cd(2+) was demonstrated. Cd(2+) binding was dramatically affected by high fatty acid loading of albumin. Analysis of the x-ray structures suggests that fatty acid binding to site 2 triggers a spring-lock mechanism, which disengages the upper (His-67Asn-99) and lower (His-247Asp-249) halves of the metal site. These findings provide a possible mechanism whereby fatty acids (and perhaps other small molecules) could influence the transport and delivery of zinc in blood.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Substitution
  • Binding Sites
  • Calcium / metabolism
  • Crystallography, X-Ray / methods
  • Histidine
  • Humans
  • Kinetics
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Mutagenesis, Site-Directed
  • Protein Structure, Secondary
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Serum Albumin / chemistry*
  • Serum Albumin / metabolism
  • Zinc / chemistry
  • Zinc / metabolism*

Substances

  • Recombinant Proteins
  • Serum Albumin
  • Histidine
  • Zinc
  • Calcium