Albumin subdomains

Figure 2. Frequency of residues of the two albumin subdomains and of the fi-bronectin module as function of their hydropathy index (see text).

Figure Interaction energy Emt (left) and stretin energy E,train (right) plotted as a function of tisoa. The results obtained for the two albumin subdomains in dififerent orientations are stained for the two albumin subdomains in different orientations are shown with empty symbol, and for the fibronectin module with full symbols. The solid lines are the best-fit lines through the origin given by eqs. (1) and (2).

We report in Figure 5 the optimized geometries obtained in the final adsorption stage. We found a very similar behaviour for both albumin subdomains and therefore we report just one case. 

Both albumin subdomains show an extensive denaturation with the formation of a monolayer of amino acids. Such a large molecular spreading on the surface is consistent with experimental data obtained for the whole protein on a hydrophobic surface [15]. On the other hand, for the fibronectin module it is more difficult to form a monolayer on the graphite surface because it contains four disulfide bridges acting as intramolecular crosslinks. We studied how such crosslinks affect or even hinder the conformational changes during the MD runs by per-... 

In the most stable state, found after optimization of many selected snapshots, the fibronectin module and the albumin subdomains optimize the surface interaction by spreading as much as possible, thus maximiz-... 

Figure 9. Pair distribution function (PDF) of the oxygen atoms of the water molecules around the backbone of the two albumin subdomains in the initial and final adsorption state (left), and around the backbone of the fibronectin module as an isolated molecule and in the final adsorption state (right).

In the present paper we review our recent work on the adsorption of two albumin subdomains and a fibronectin module on a graphite surface by atomistic simulations through energy minimizations and molecular dynamics runs. We adopted a simulation strategy in two-steps to study the initial and the final adsorption state on a bare surface in a dielectric medium and in the explicit presence of the solvent. 

Viallet, P. M. Vo-Dinh, T. Rihou, A. C. Vigo, J. Salmon, J. M. Native fluorescence and Mag-indo-1-protein interaction as tools for probing unfolding and refolding sequences of the bovine serum albumin subdomain in the presence of guanidine hydrochloride. J. Protein Chem. 2000,19, 431-439. 

Fig. 3.17. The crystal structure of human serum albumin (HSA) complexed with four molecules ofmyristic acid (from lbj5.pdb [121][122]). The picture shows the domains (I—III) and subdomains (A and B) of HSA. The primary hydrolytic site is located in subdomain IIIA, and two others probably in subdomain IIA. 

J Sowell, JC Mason, L Strekowski, G Patonay. Binding constant determination of drugs toward subdomain IIIA of human serum albumin by near-infrared dye-displacement capillary electrophoresis. Electrophoresis 22 2512-2517, 2001. 

Due possibly to the above mentioned heterogeneity, there is some variability with regard to the conclusions reached by various workers concerning the structure and configuration of bovine serum albumin. Brown (1977) proposed two possible models based on the primary sequence of the protein. He demonstrated that the molecule could possess a triple domain structure with three very similar domains residues 1-190, 191-382, and 383-582. Each domain could then consist of five helical rods of about equal length arranged either in a parallel or an antiparallel manner. His second model consisted of the following (1) a lone subdomain (1-101) (2) a pair of antiparallel subdomains, with their hydrophobic faces toward each other (113-287) (3) another pair of subdomains (314-484) and (4) a lone subdomain (512-582). These structures are supported by the observed helical content of bovine... 

Human serum albumin (HSA) is an important transporter of fatty acids, metabolites, drugs, and organic compounds in the circulatory system [93, 94], It is a single polypeptide chain consisting of 585 amino acids. Under physiological conditions (pH 7), HSA adopts a heart-shaped three-dimensional (3D) structure with three homologous domains I—III (Fig. 14) each domain contains two subdomains A and B, which consist of four and six a-helices, respectively [95, 96]. The X-ray structure shows that two halves of the albumin molecule... 

MRI CAs meet a variety of biomolecules in physiological environments, and may interact with proteins, human serum albumin (HSA), enzymes, and receptors. The binding of CAs to HSA is widely studied because it is the most abundant protein in blood plasma. HSA has a molecular weight of 66 kDa, a concentration of approximately 0.64 mM, and with two major binding sites, which are subdomains of IIA and III A [63]. 

The vast majority of ligands in Table V are bound in one or both sites within specialized cavities of subdomains IIA and IIIA. At this time the binding locations of several key compounds, historically used as markers in drug or ligand displacement interactions, have been determined at various resolutions (Table VI). Clearly, from Table VI it can be seen that IIIA appears to possess the primary binding activity for albumin whereas IIA is more specialized. 

Fig. 6. Section of the 6.0-A electron density of subdomain IIIB. Helical rods of density 8.0 to 10 A in diameter, indicative of the a-helical structure of serum albumin, were the dominant features of the electron density. Reproduced with permission from Carter et al. (1989) and the American Association for the Advancement of Science (AAAS).

Fig. 7. Stereo view of human serum albumin illustrating the overall topology and secondary structure. The positions of the 17 disulfides and the side chain of Cys-34 are shown in red. Structurally, HSA consists of 28 helices, which range in size from 5 to 31 amino acids in length and which can be grouped into 10 principal helices within each domain. The positions of the two major binding sites of HSA, located within subdomains IIA and IIIA, are illustrated with the ligand 2,3,5-triiodobenzoic acid, shown in white. Figure drawn using program RIBBONS (Carson, 1987).

Tian JN, Liu JQ, Xie JP, Yao XJ, Hu ZD, Chen XG. Binding of wogonin to human serum albumin a common binding site of wogonin in subdomain IIA,J Photochem. Photobiol B 2004 74 39-45. 

Figure 4 The structure of human albumin, showing the domains, subdomains and cys-34.

The phenomenon of the rapid adsorption of albumin onto a PEUN surface may be associated with hydrophobic and hydrophilic interactions of the PEUN surface with some sequences of relatively hydrophobic amino acid residues in the interior of albumin. An albumin molecule is composed of three-subdomains (15). There are two gaps between the subdomains. One is a hydrophobic pocket with an affinity constant, K3=1.1x10 M for stearic acid the other is an intermediate hydrophobic pocket with K =1.5xl0 M for bilirubin (16). Perhaps the structure of adsorbed albumin in contact with a PEUN surface is composed of hydrophobic and hydrophilic regions corresponding or complementary to those of the PEUN surface, even though the exterior of native albumin is rich in hydrophilic amino acid side chains. 

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