The three-dimensional structure of human serum albumin has been determined crystallographically to a resolution of 2.8 A. It comprises three homologous domains that assemble to form a heart-shaped molecule. Each domain is a product of two subdomains that possess common structural motifs. The principal regions of ligand binding to human serum albumin are located in hydrophobic cavities in subdomains IIA and IIIA, which exhibit similar chemistry. The structure explains numerous physical phenomena and should provide insight into future pharmacokinetic and genetically engineered therapeutic applications of serum albumin.

Atomic structure and chemistry of human serum albumin.

Publisher Summary This chapter provides an insight of the findings of past significant papers with the current knowledge of the recently determined high resolution X-ray structure of serum albumin. The most outstanding property of albumin is its ability to bind reversibly an incredible variety of ligands. The sequences of all albumins are characterized by a unique arrangement of disulfide double loops that repeat as a series of triplets. Albumin belongs to a multigene family of proteins that includes α- fetoprotein (AFP) and vitamin D-binding protein (VDP), also known as G complement (Gc) protein. Although AFP is considered the fetal counterpart of albumin, its binding properties are distinct and it is suggested that AFP may have a higher affinity for some unknown ligands important for fetal development. Domain structure and the arrangement of the disulfides, the surface charge distribution, and the conformational flexibility of the albumin molecule are described. The nature of ligand binding, including small organics, long-chain fatty acids, and metals, to multiple sites on the albumin molecule is clearly depicted. The chapter concludes with the perceptive comments on future directions being taken to explore the structure and function of this fascinating protein.

Structure of serum albumin.

Albumin as a drug carrier: design of prodrugs, drug conjugates and nanoparticles.

A new triclinic crystal form of human serum albumin (HSA), derived either from pool plasma (pHSA) or from a Pichia pastoris expression system (rHSA), was obtained from polyethylene glycol 4000 solution. Three-dimensional structures of pHSA and rHSA were determined at 2.5 A resolution from the new triclinic crystal form by molecular replacement, using atomic coordinates derived from a multiple isomorphous replacement work with a known tetragonal crystal form. The structures of pHSA and rHSA are virtually identical, with an r.m. s. deviation of 0.24 A for all Calpha atoms. The two HSA molecules involved in the asymmetric unit are related by a strict local twofold symmetry such that the Calpha atoms of the two molecules can be superimposed with an r.m.s. deviation of 0.28 A in pHSA. Cys34 is the only cysteine with a free sulfhydryl group which does not participate in a disulfide linkage with any external ligand. Domains II and III both have a pocket formed mostly of hydrophobic and positively charged residues and in which a very wide range of compounds may be accommodated. Three tentative binding sites for long-chain fatty acids, each with different surroundings, are located at the surface of each domain.

Crystal structure of human serum albumin at 2.5 A resolution.

Protein adhesion plays a major role in determining the biocompatibility of materials. The first stage of implant integration is the adhesion of protein followed by cell attachment. Surface modification of implants (surface chemistry and topography) to induce and control protein and cell adhesion is currently of great interest. This communication presents data on protein adsorption (bovine serum albumin and fibrinogen) onto model hydrophobic (CH3) and hydrophilic (OH) surfaces, investigated using a quartz crystal microbalance (QCM) and grazing angle infrared spectroscopy. Our data suggest that albumin undergoes adsorption via a single step whereas fibrinogen adsorption is a more complex, multistage process. Albumin has a stronger affinity toward the CH3 compared to OH terminated surface. In contrast, fibrinogen adheres more rapidly to both surfaces, having a slightly higher affinity toward the hydrophobic surface. Conformational assessment of the adsorbed proteins by grazing angle infrared spectroscopy (GA...

Interpretation of Protein Adsorption: Surface-Induced Conformational Changes

The three-dimensional structure of human serum albumin has been solved at 6.0 angstrom (A) resolution by the method of multiple isomorphous replacement. Crystals were grown from solutions of polyethylene glycol in the infrequently observed space group P42(1)2 (unit cell constants a = b = 186.5 +/- 0.5 A and c = 81.0 +/- 0.5 A) and diffracted x-rays to lattice d-spacings of less than 2.9 A. The electron density maps are of high quality and revealed the structure as a predominantly alpha-helical globin protein in which the course of the polypeptide can be traced. The binding loci of several organic compounds have been determined.

https://science.sciencemag.org/content/sci/244/4909/1195.full.pdf

Three-dimensional structure of human serum albumin.

The amino-acid sequence and three-dimensional structure of equine serum albumin have been determined. The amino-acid sequence was deduced from cDNA isolated from equine liver. Comparisons of the primary structure of equine serum albumin with human serum albumin and bovine serum albumin reveal 76.1% and 73.9% sequence identity, respectively. The three-dimensional structure was determined crystallographically by the molecular-replacement method using molecular coordinates from the previously determined structure of human serum albumin, to a resolution of 0.27 nm. In accordance with the primary structure, the three-dimensional structures are highly conserved. There is a root-mean-square difference between alpha-carbons of the two structures of 0.201 nm. The association constants (Ka) for the binding of 2,3,5-triiodobenzoic acid were determined by ultrafiltration methods for equine and human serum albumins to be approximately 10(4) M-1 and 10(5) M-1, respectively. Crystallographic studies of equine serum albumin reveal two binding sites for 2,3,5-triiodobenzoic acid identical with those previously reported for human serum albumin which are located within subdomains in IIA and IIIA. Details and comparisons of the binding chemistry are discussed.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1993.tb18024.x

Pamela D. Twigg

Papers

Three-dimensional structure of human serum albumin.

X-ray and primary structure of horse serum albumin (Equus caballus) at 0.27-nm resolution.

Protein crystal growth aboard the U.S. space shuttle flights STS-31 and STS-32.