The article presents the atomic structure and chemistry of human serum albumin (HSA), determined through crystallographic analysis. The three-dimensional structure of HSA was resolved at a resolution of 2.8 Å, revealing three homologous domains that form a heart-shaped molecule. Each domain consists of two subdomains with common structural motifs. The primary ligand-binding regions are located in hydrophobic cavities in subdomains IIA and IIIA, which exhibit similar chemistry. The structure provides insights into the physical properties and potential applications of HSA in pharmacokinetics and therapeutic development. The structure of HSA is composed of 585 amino acids, with 17 disulphide bridges and one free thiol. The disulphides are arranged in a repeating series of nine loop-link-loop structures. The amino acid sequence is highly conserved among HSA, bovine, and rat albumins, suggesting a common ancestral protein. The structure of HSA was determined using crystallographic methods, with the wild-type HSA resolved at 3.1 Å and the recombinant form (rHSA) at 2.8 Å. The structure reveals that HSA has a helical topology with 67% of the molecule being helical, and the remaining in turns and extended polypeptide. The study also examines the binding of various ligands to HSA, including 2,3,5-triiodobenzoic acid (TIB), which binds preferentially to the IIIA subdomain. The binding sites in IIA and IIIA are distinct, with TIB binding in a hydrophobic crevice in the cavity. The carboxylate group of TIB interacts with several residues, and the binding site is characterized by an asymmetric distribution of hydrophobic and hydrophilic residues. The structure of HSA has implications for understanding the function and properties of albumin, including its role in transporting various ligands across organ-circulatory interfaces. The study also highlights the importance of the disulphide bridges in maintaining the structural integrity of HSA and their role in ligand binding. The findings contribute to the understanding of the molecular mechanisms underlying the function of albumin and its potential applications in medicine and biotechnology.The article presents the atomic structure and chemistry of human serum albumin (HSA), determined through crystallographic analysis. The three-dimensional structure of HSA was resolved at a resolution of 2.8 Å, revealing three homologous domains that form a heart-shaped molecule. Each domain consists of two subdomains with common structural motifs. The primary ligand-binding regions are located in hydrophobic cavities in subdomains IIA and IIIA, which exhibit similar chemistry. The structure provides insights into the physical properties and potential applications of HSA in pharmacokinetics and therapeutic development. The structure of HSA is composed of 585 amino acids, with 17 disulphide bridges and one free thiol. The disulphides are arranged in a repeating series of nine loop-link-loop structures. The amino acid sequence is highly conserved among HSA, bovine, and rat albumins, suggesting a common ancestral protein. The structure of HSA was determined using crystallographic methods, with the wild-type HSA resolved at 3.1 Å and the recombinant form (rHSA) at 2.8 Å. The structure reveals that HSA has a helical topology with 67% of the molecule being helical, and the remaining in turns and extended polypeptide. The study also examines the binding of various ligands to HSA, including 2,3,5-triiodobenzoic acid (TIB), which binds preferentially to the IIIA subdomain. The binding sites in IIA and IIIA are distinct, with TIB binding in a hydrophobic crevice in the cavity. The carboxylate group of TIB interacts with several residues, and the binding site is characterized by an asymmetric distribution of hydrophobic and hydrophilic residues. The structure of HSA has implications for understanding the function and properties of albumin, including its role in transporting various ligands across organ-circulatory interfaces. The study also highlights the importance of the disulphide bridges in maintaining the structural integrity of HSA and their role in ligand binding. The findings contribute to the understanding of the molecular mechanisms underlying the function of albumin and its potential applications in medicine and biotechnology.