1ij8
CRYSTAL STRUCTURE OF LITE AVIDIN-BNI COMPLEX
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OverviewOverview
Avidin and its bacterial analogue streptavidin exhibit similarly high, affinities toward the vitamin biotin. The extremely high affinity of these, two proteins has been utilized as a powerful tool in many biotechnological, applications. Although avidin and streptavidin have similar tertiary and, quaternary structures, they differ in many of their properties. Here we, show that avidin enhances the alkaline hydrolysis of biotinyl, p-nitrophenyl ester, whereas streptavidin protects this reaction even, under extreme alkaline conditions (pH > 12). Unlike normal enzymatic, catalysis, the hydrolysis reaction proceeds as a single cycle with no, turnover because of the extremely high affinity of the protein for one of, the reaction products (i.e. free biotin). The three-dimensional crystal, structures of avidin (2 A) and streptavidin (2.4 A) complexed with the, amide analogue, biotinyl p-nitroanilide, as a model for the p-nitrophenyl, ester, revealed structural insights into the factors that enhance or, protect the hydrolysis reaction. The data demonstrate that several, molecular features of avidin are responsible for the enhanced hydrolysis, of biotinyl p-nitrophenyl ester. These include the nature of a decisive, flexible loop, the presence of an obtrusive arginine 114, and a newly, formed critical interaction between lysine 111 and the nitro group of the, substrate. The open conformation of the loop serves to expose the, substrate to the solvent, and the arginine shifts the p-nitroanilide, moiety toward the interacting lysine, which increases the electron, withdrawing characteristics and consequent electrophilicity of the, carbonyl group of the substrate. Streptavidin lacked such molecular, properties, and analogous interactions with the substrate were, consequently absent. The information derived from these structures may, provide insight into the action of artificial protein catalysts and the, evolution of catalytic sites in general.
About this StructureAbout this Structure
1IJ8 is a Single protein structure of sequence from Gallus gallus with NDG and BNI as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Chicken avidin exhibits pseudo-catalytic properties. Biochemical, structural, and electrostatic consequences., Huberman T, Eisenberg-Domovich Y, Gitlin G, Kulik T, Bayer EA, Wilchek M, Livnah O, J Biol Chem. 2001 Aug 24;276(34):32031-9. Epub 2001 Jun 6. PMID:11395489
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