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J. Biol. Chem., Vol. 281, Issue 46, 35454-35466, November 17, 2006

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Solution Structures and Backbone Dynamics of a Flavodoxin MioC from Escherichia coli in both Apo- and Holo-forms

IMPLICATIONS FOR COFACTOR BINDING AND ELECTRON TRANSFER^*

Yunfei Hu, You Li^¶, Xinxin Zhang, Xianrong Guo^¶, Bin Xia^¶, and Changwen Jin^¶1

From the Beijing Nuclear Magnetic Resonance Center, College of Life Sciences, and ^¶College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China

Flavodoxins play central roles in the electron transfer involving various biological processes in microorganisms. The mioC gene of Escherichia coli encodes a 16-kDa flavodoxin and locates next to the chromosomal replication initiation origin (oriC). Extensive researches have been carried out to investigate the relationship between mioC transcription and replication initiation. Recently, the MioC protein was proposed to be essential for the biotin synthase activity in vitro. Nevertheless, the exact role of MioC in biotin synthesis and its physiological function in vivo remain elusive. In order to understand the molecular basis of the biological functions of MioC and the cofactor-binding mechanisms of flavodoxins, we have determined the solution structures of both the apo- and holo-forms of E. coli MioC protein at high resolution by nuclear magnetic resonance spectroscopy. The overall structures of both forms consist of an / sandwich, which highly resembles the classical flavodoxin fold. However, significant diversities are observed between the two forms, especially the stabilization of the FMN-binding loops and the notable extension of secondary structures upon FMN binding. Structural comparison reveals fewer negative charged and aromatic residues near the FMN-binding site of MioC, as compared with that of flavodoxin 1 from E. coli, which may affect both the redox potentials and the redox partner interactions. Furthermore, the backbone dynamics studies reveal the conformational flexibility at different time scales for both apo- and holo-forms of MioC, which may play important roles for cofactor binding and electron transfer.

Received for publication, August 2, 2006 , and in revised form, September 1, 2006.

The atomic coordinates and structure factors (code 2HNA and 2HNB) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

^* This research was supported by National Natural Science Foundation of China Grant 30125009 (to B. X.) and Grant 30325010 (to C. J.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Tables 1 and 2.

¹ To whom correspondence should be addressed: Beijing Nuclear Magnetic Resonance Center, Peking University, Beijing 100871, China. Tel.: 86-10-6275-6004; Fax: 86-10-6275-3790; E-mail: changwen{at}pku.edu.cn.

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