Role of Tyr84 in controlling the reactivity of Cys34 of human albumin

Abstract

Cys34 in domain I of the three‐domain serum protein albumin is the binding site for a wide variety of biologically and clinically important small molecules, provides antioxidant activity, and constitutes the largest portion of free thiol in blood. Analysis of X‐ray structures of albumin reveals that the loop containing Tyr84 occurs in multiple conformations. In structures where the loop is well defined, there appears to be an H‐bond between the OH of Tyr84 and the sulfur of Cys34. We show that the reaction of 5,5′‐dithiobis(2‐nitrobenzoic acid) (DTNB) with Tyr84Phe mutant albumin is approximately four times faster than with the wild‐type protein between pH 6 and pH 8. In contrast, the His39Leu mutant reacts with DTNB more slowly than the wild‐type protein at pH < 8, but at a similar rate at pH 8. Above pH 8 there is a dramatic increase in reactivity for the Tyr84Phe mutant. We also report 1H NMR studies of disulfide interchange reactions with cysteine. The tethering of the two loops containing Tyr84 and Cys34 not only appears to control the redox potential and accessibility of Cys34, but also triggers the transmission of information about the state of Cys34 throughout domain I, and to the domainI/II interface.

Site-Specific Chemical Modification of Human Serum Albumin with Polyethylene Glycol Prolongs Half-life and Improves Intravascular Retention in Mice

“…Crystallographic studies of albumin show that Cys34 is buried in a shallow crevice, 9.5Å deep. 27) This may explain why the modification yield at Cys34 was only about 50%. The attachment of PEG was proved to be selective to the unique thiol group of HSA by a two-step method in this study.…”

Structure, Properties, and Engineering of the Major Zinc Binding Site on Human Albumin

“…Albumin is known to exhibit esterase-like activity, but this has previously 99 mutations on the two low-field shifted resonances labeled 1 and 4 allows these two peaks to be assigned to His 67 and His 247 . His 3 (55) and His 39 (56) have been assigned previously and are labeled 11 and 7, respectively. The bottom spectrum demonstrates the effect of zinc addition on the His H-⑀1 NMR resonances of wild-type rHA.…”

Oxidation of the albumin thiol to sulfenic acid and its implications in the intravascular compartment

“…According to the model of Christodoulou et al (14,15), the Cys34 thiol exists in two conformations, and the reduced thiol predominates in a buried conformation that shifts to an exposed one upon oxidation. In addition, the two close groups of His39 and Tyr84 affect the reactivity of the thiol (16). Also, HSA presents pH-dependent structural transitions that impact on thiol reactivity (17).…”