title: Plasma free fatty acid levels influence Zn(2+) -dependent histidine-rich glycoprotein-heparin interactions via an allosteric switch on serum albumin.
abstract: BACKGROUND
  Histidine-rich glycoprotein (HRG) regulates coagulation through its ability to bind and neutralize heparins. HRG associates with Zn(2+) to stimulate HRG-heparin complex formation. Under normal conditions, the majority of plasma Zn(2+) associates with human serum albumin (HSA). However, free fatty acids (FFAs) allosterically disrupt Zn(2+) binding to HSA. Thus, high levels of circulating FFAs, as are associated with diabetes, obesity, and cancer, may increase the proportion of plasma Zn(2+) associated with HRG, contributing to an increased risk of thrombotic disease.
  
  
  OBJECTIVE
  To characterize Zn(2+) binding by HRG, examine the influence that FFAs have on Zn(2+) binding by HSA, and establish whether FFA-mediated displacement of Zn(2+) from HSA may influence HRG-heparin complex formation.
  
  
  METHODS
  Zn(2+) binding to HRG and to HSA in the presence of different FFA (myristate) concentrations were examined by isothermal titration calorimetry (ITC) and the formation of HRG-heparin complexes in the presence of different Zn(2+) concentrations by both ITC and ELISA.
  
  
  CONCLUSIONS
  We found that HRG possesses 10 Zn(2+) sites (K' = 1.63 × 10(5) ) and that cumulative binding of FFA to HSA perturbed its ability to bind Zn(2+) . Also Zn(2+) binding was shown to increase the affinity with which HRG interacts with unfractionated heparins, but had no effect on its interaction with low molecular weight heparin (~ 6850 Da). [Correction added on 1 December 2014, after first online publication: In the preceding sentence, "6850 kDa" was corrected to "6850 Da".] Speciation modeling of plasma Zn(2+) based on the data obtained suggests that FFA-mediated displacement of Zn(2+) from serum albumin would be likely to contribute to the development of thrombotic complications in individuals with high plasma FFA levels.
authors.affiliation: School of Medicine, University of St Andrews, St Andrews, UK.
authors.forename: O
authors.initials: O
authors.lastname: Kassaar
authors.forename: U
authors.initials: U
authors.lastname: Schwarz-Linek
authors.forename: C A
authors.initials: CA
authors.lastname: Blindauer
authors.forename: A J
authors.initials: AJ
authors.lastname: Stewart
mesh_terms: D000818:Animals; D000925:Anticoagulants / Q000097:blood*; D001665:Binding Sites; D001667:Binding, Competitive; D005230:Fatty Acids, Nonesterified / Q000009:adverse effects / Q000097:blood*; D006493:Heparin / Q000097:blood*; D006495:Heparin, Low-Molecular-Weight / Q000097:blood; D006801:Humans; D008958:Models, Molecular; D019814:Myristic Acid / Q000009:adverse effects / Q000097:blood*; D011485:Protein Binding; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D011817:Rabbits; D012307:Risk Factors; D012709:Serum Albumin / Q000737:chemistry / Q000378:metabolism*; D000075462:Serum Albumin, Human; D013927:Thrombosis / Q000097:blood / Q000139:chemically induced; D015032:Zinc / Q000097:blood*; D000099053:Histidine-Rich Glycoprotein
chemical_list: C422455:ALB protein, human; D000925:Anticoagulants; D005230:Fatty Acids, Nonesterified; D006495:Heparin, Low-Molecular-Weight; D011506:Proteins; D012709:Serum Albumin; D000099053:Histidine-Rich Glycoprotein; D019814:Myristic Acid; D006493:Heparin; D015032:Zinc; D000075462:Serum Albumin, Human
keywords: fatty acids; heparin; histidine-rich glycoprotein; plasma albumin; zinc