Crystal structural analysis of human serum albumin complexed with hemin and fatty acid

Abstract

Background: Human serum albumin (HSA) is an abundant plasma protein that binds a wide variety of hydrophobic ligands including fatty acids, bilirubin, thyroxine and hemin. Although HSAheme complexes do not bind oxygen reversibly, it may be possible to develop modified HSA proteins or heme groups that will confer this ability on the complex.

Reversible two-step unfolding of heme–human serum albumin: a 1H-NMR relaxometric and circular dichroism study

“…An appropriate aliquot of the myristate solution was then mixed with 1.0 9 10 -4 M heme-HSA to achieve the desired myristate concentration. Then, the heme-HSA-myristate complex was incubated for 1 h at room temperature under continuous stirring [13]. Lastly, the pH was adjusted to pH 7.0 by adding few microliters of 1.0 9 10 -1 M HCl or 1.0 9 10 -1 M NaOH.…”

“…In sites FA1-FA5 the carboxylate moiety of FAs is anchored by electrostatic/polar interactions; in contrast, sites FA6 and FA7 do not display clear evidence of polar interactions that keep in place the carboxylate head of the FA, thus suggesting that sites FA6 and FA7 are low-affinity FA binding sites [3,4,[6][7][8][9][10]. One of the FA binding sites (FA1) has evolved to selectively bind heme with high affinity (K d = 1.0 9 10 -8 M [11]) with the tetrapyrrole ring arranged in a D-shaped cavity limited by Tyr138 and Tyr161 residues that provide p-p stacking interaction with the porphyrin and supply a donor oxygen (from Tyr161) for the Fe(III) heme iron [10][11][12][13][14]. In turn, heme binding to HSA endows the protein with heme-based reactivity [4,15] and spectroscopic properties [16][17][18][19][20][21].…”

“…Binding of FAs to HSA is known to determine a conformational change in the protein structure [3,5,13,20].…”

Evidence for pH-dependent multiple conformers in iron(II) heme–human serum albumin: spectroscopic and kinetic investigation of carbon monoxide binding

“…The FA1 binding site has been shown to be the primary binding site of several ligands, including the heme [14,33]. There is increasing evidence that FA1 has evolved to selectively bind iron(III) heme with high affinity (K d * 10 -8 M) [14-16, 29, 33].…”

“…The iron(III) heme propionates protrude from the pocket, pointing toward the interface between domains I and III and are stabilized by salt bridges with His146 and Lys190. A weak coordination between the iron(III) heme and the phenolic oxygen atom of the Tyr161 residue (Fe-O Tyr161 distance 2.73 Å ) was suggested by crystallography [14,33] and further confirmed by resonance Raman spectroscopy [34]. Iron(III) heme is secured to HSA by the long IA-IB connecting loop that fits into the cleft opening [14-16, 29, 33, 34].…”