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Plasma free fatty acid levels influence Zn 2+ ‐dependent histidine‐rich glycoprotein–heparin interactions via an allosteric switch on serum albumin
Author(s) -
Kassaar O.,
SchwarzLinek U.,
Blindauer C. A.,
Stewart A. J.
Publication year - 2015
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/jth.12771
Subject(s) - isothermal titration calorimetry , chemistry , heparin , histidine , human serum albumin , zinc , titration , albumin , biochemistry , amino acid , inorganic chemistry , organic chemistry
Summary 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 ( FFA s) allosterically disrupt Zn 2+ binding to HSA . Thus, high levels of circulating FFA s, 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. Objectives To characterize Zn 2+ binding by HRG , examine the influence that FFA s 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 . Results and 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.