Albumin crystal structure

Fig. 4. Backscattered Raman and ROA spectra of the n-helical protein human serum albumin in H20 (top pair) and the /3-sheet protein jack bean concanavalin A in acetate buffer solution at pH 5.4, together with MOLSCRIPT diagrams (Kraulis, 1991) of their X-ray crystal structures (PDB codes lao6 and 2cna). 

According to the PDB X-ray crystal structure 1 ao6, human serum albumin contains 69.2% o -helix and 1.7% 3io-helix, the rest being made up of turns and long loops. The amide I ROA couplet centered at 1650 cm-1 (Fig. 4), which is negative at low wavenumber and positive at high,... 

Curry, S., Mandelkow, H., Brick, P. and Franks, N. (1998) Crystal structure of human serum albumin complexed with fatty acid reveals an asymmetric distribution of binding sites. Nature Structural Biology 5, 827-835. 

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. 

I. Petitpas, T. Grime, A. A. Bhattacharya, S. Curry, Crystal Structures of Human Serum Albumin Complexed with Monounsaturated and Polyunsaturated Fatty Acids , J. Mol. Biol. 2001, 314, 955-960. 

Twine, S., East, M., and Curry, S. Crystal structure analysis of warfarin binding to human serum albumin. Anatomy of dmg site I. /. Biol. Chem. 

The crystal structure of human albumin located Cysteine-34 at the turn between helices h2 and h3 with the side chain sulfhydryl group oriented toward the protein interior, consistent with EPR studies suggesting that it is 950 pm below the surface. Sadler has demonstrated by H NMR studies that the cys-34 residue must move outward from the crevice created by the helices before it can react to form disulfide bonds or bind to Et3PAu+ derived from auranofin. These structural observations are consistent with the kinetic mechanism for the reactions of albumin with auranofin and its triisopropylphosphine analogue, which revealed a slow crevice opening reaction in equilibrium between open and closed forms of albumin. The kinetic model accounts for a process that is first order in protein when the auranofin is present in excess. 

Crystal structure of human serum albumin at 2.5 A resolution. Protein Eng. 12 439-46. 

Examinations of the crystal structures of HSA and ESA in this vicinity indicated that Cys-34 is located in a crevice on the surface of the protein and that the reactive sulfur is somewhat protected by several residues (Fig. 17, see color insert). In HSA, Cys-34 is in close proximity to Glu-82 and His-39. In ESA the Cys environment is also protected but, with the exception of His-39, which (along with Cys-34) is conserved in mammalian albumin sequences (Table II), it involves contributions from different amino acids. Thus, one may expect that His-39 plays a major role in the enhanced reactivity of the free sulfhydryl. Interestingly, in the crystal structure of albumin complexed with three or more long-chain fatty acids. 

For the construction of artificial metalloproteins, protein scaffolds should be stable, both over a wide range of pH and organic solvents, and at high temperature. In addition, crystal structures of protein scaffolds are crucial for their rational design. The proteins reported so far for the conjugation of metal complexes are listed in Fig. 1. Lysozyme (Ly) is a small enzyme that catalyzes hydrolysis of polysaccharides and is well known as a protein easily crystallized (Fig. la). Thus, lysozyme has been used as a model protein for studying interactions between metal compounds and proteins [13,14,42,43]. For example, [Ru(p-cymene)] L [Mn(CO)3l, and cisplatin are regiospecificaUy coordinated to the N = atom of His 15 in hen egg white lysozyme [14, 42, 43]. Serum albumin (SA) is one of the most abundant blood proteins, and exhibits an ability to accommodate a variety of hydrophobic compounds such as fatty acids, bilirubin, and hemin (Fig. lb). Thus, SA has been used to bind several metal complexes such as Rh(acac)(CO)2, Fe- and Mn-corroles, and Cu-phthalocyanine and the composites applied to asymmetric catalytic reactions [20, 28-30]. 

Non-covalent insertion of several modified metal cofactors and synthetic metal complexes into protein cavities such as serum albumin (SA) and Mb has been reported [5, 24, 28, 30, 69], If synthetic metal complexes, whose structures are very different from native cofactors, can be introduced into protein cages, the bioconjugation of metal complexes will be applicable to many proteins and metal complexes. Mn(corrole) and Cn(phthalocyanine) are inserted into SA by non-covalent interactions and the composites catalyze asymmetric sulfoxidation and Diels-Alder reactions with up to 74 and 98% ee, respectively (Fig. 2c) [28, 30], Since the heme is coordinated to Tyrl61 in the albumin cavity, determined by X-ray crystal structure [20], it is expected that both Mn(corrole) and Cu(phtalocyanine) are also bound to albumin with the same coordination. The incorporation of synthetic metal complexes in protein cavities using these methods is a powerful approach for asymmetric catalytic reactions. However, there are still some difficulties in further design of the composites for improving reactivities and understanding reaction mechanisms because detailed structural analyses are not available for most of the composites. 

Sugio S, Kashima A, Mochizuki S, Noda M, Kobayashi K. Crystal structure of human serum albumin at 2.5 A resolution. Protein Eng 1999 12(6) 439-46. 

Figure 5.5 (Plate 1) (A) Crystal structure of human albumin (PDB ID 1A06) with helix 1-3 and Cys34 (space-filling model) highlighted. Color code cyan, residues 5-61 (containing helix 10-3) yellow, Cys34. (B) A model for structural changes induced by the Au drug in domain I of albumin. Adapted with permission from I C. Christodoulou et al, FEES Lett. 376, 1 (1995) [119].

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