Anion-mediated Fe3+ Release Mechanism in Ovotransferrin C-lobe

Kimihiko, Mizutani and Muralidhara, B. K. and Honami, Yamashita and Satoshi, Tabata (2001) Anion-mediated Fe3+ Release Mechanism in Ovotransferrin C-lobe. Journal of Biological Chemistry, 276 (28). pp. 35940-35946.

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Abstract

The differential properties of anion-mediated Fe3_ release between the N- and C-lobes of transferrins have been a focus in transferrin biochemistry. The structural and kinetic characteristics for isolated lobe have, however,been documented with the N-lobe only. Here we demonstrate for the first time the quantitative Fe3_ release kinetics and the anion-binding structure for the isolated C-lobe of ovotransferrin. In the presence of pyrophosphate, sulfate, and nitrilotriacetate anions, the C-lobe released Fe3_ with a decelerated rate in a single exponential progress curve, and the observed first order rate constants displayed a hyperbolic profile as a function of the anion concentration. The profile was consistent with a newly derived single-pathway Fe3_ release model in which the holo form is converted depending on the anion concentration into a “mixed ligand” intermediate that releases Fe3_. The apo C-lobe was crystallized in ammonium sulfate solution, and the structure determined at 2.3 Å resolution demonstrated the existence of a single bound SO4 2_ in the interdomain cleft, which interacts directly with Thr461-OG1, Tyr431-OH, and His592-NE2 and indirectly with Tyr524-OH. The latter three groups are Fe3_-coordinating ligands, strongly suggesting the facilitated Fe3_ release upon the anion occupation at this site. The SO4 2_ binding structure supported the single-pathway kinetic model.

Item Type:	Article
Uncontrolled Keywords:	C-lobes transferrins iron-binding proteins
Subjects:	500 Natural Sciences and Mathematics > 04 Chemistry and Allied Sciences > 29 Protein Chemistry 600 Technology > 08 Food technology > 16 Nutritive value > 03 Proteins
Divisions:	Protein Chemistry and Technology
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	10 Jan 2008 04:43
Last Modified:	28 Dec 2011 09:32
URI:	http://ir.cftri.res.in/id/eprint/1624

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