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Pyrexia and acidosis act independently of neutrophil elastase reactive center loop cleavage to effect cortisol release from corticosteroid‐binding globulin
Author(s) -
Meyer Emily J.,
Torpy David J.,
Chernykh Anastasia,
ThaysenAndersen Morten,
Nenke Marni A.,
Lewis John G.,
Rajapaksha Harinda,
Rankin Wayne,
Polyak Steven W.
Publication year - 2020
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.3982
Subject(s) - transcortin , chemistry , medicine , endocrinology , elastase , ligand (biochemistry) , glucocorticoid , biochemistry , biology , globulin , receptor , enzyme
Corticosteroid‐binding globulin (CBG) transports cortisol and other steroids. High‐affinity CBG (haCBG) undergoes proteolysis of the reactive center loop (RCL) by neutrophil elastase (NE) altering conformation to low‐affinity CBG (laCBG). Elevated temperature reduces CBG:cortisol binding affinity. Surface plasmon resonance was used to determine binding profiles of 19 steroids to haCBG and laCBG at 25, 37, and 39°C mimicking pyrexia and pH 7.4 and 7.0 mimicking acidosis, pathophysiological conditions relevant to sepsis. An expected 4–8‐fold reduction in affinity for cortisol, cortisone, corticosterone, 11‐deoxycortisol, progesterone, 17‐hydroxyprogesterone, and prednisolone occurred with NE‐mediated haCBG‐to‐laCBG conversion. CBG:cortisol binding affinity was further reduced 3.5‐fold at 39°C relative to 37°C, binding affinity was also reduced by acidosis for both haCBG and laCBG. Using a conformational antibody generated against the RCL, we confirmed RCL antibody binding was eliminated by NE cleavage, but preserved in pyrexia and acidosis. Molecular modeling studies performed at 40°C confirmed a critical role for Trp371, positioned within the steroid‐binding pocket, in ligand binding. These studies demonstrated CBG binding affinity to range of steroids is ligand specific and is reduced with NE‐mediated haCBG‐to‐laCBG transition. Reduced CBG:cortisol binding occurs with increased temperature and in acidosis. Increased flexibility of the Trp371 side chain is proposed in the thermo‐coupling mechanism of cortisol release. The synergy of NE cleavage, pyrexia, and acidosis on CBG:cortisol binding may serve to enhance cortisol delivery to the interstitial space in inflammation.