Structure of the month - February 2007

J. Biol. Chem. Vol. 281, October 2006, Pages 30186-30194

Structure of the Molybdenum Cofactor Carrier Protein

Katrin Fischer^1,5, Angel Llamas^1,2, Manuel Tejada-Jimenez^1,2, Nils Schrader^1,3, Jochen Kuper⁴, Farid S. Ataya², Aurora Galvan², Ralf R. Mendel¹, Emilio Fernandez², and Guenter Schwarz^1,5,*

^{1 Institute of Plant Biology, Technical University Braunschweig, 38106 Braunschweig, Germany
2 Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, Córdoba 14071, Spain
3 Department of Structural Biology, Max-Planck-Institute of Molecular Physiology, 44247 Dortmund, Germany
4 European Molecular Biology Laboratory (EMBL) outstation, 22603 Hamburg, Germany
5 Institute of Biochemistry, University of Cologne, 50674 Cologne, Germany}

*Correspondence:
Guenter Schwarz
Institut für Biochemie, Universität zu Köln
Otto-Fischer-Str. 12-14
D-50674 Köln, Germany
Phone: 49-221-470-6432
Fax: 49-221-470-6731
E-mail: gschwarz@uni-koeln.de

Abstract

The molybdenum cofactor (Moco) forms the catalytic site in all eukaryotic molybdenum enzymes and is synthesized by a conserved multi-step biosynthetic pathway. The mechanism of transfer, storage, and insertion of Moco into the appropriate apo-enzyme is poorly understood. Recently a unique Moco carrier protein (MCP) has been identified and characterized in the eukaryotic green algae Chlamydomonas reinhardtii (Ataya et al., 2003; Witte et al., 1998).

We have determined the crystal structure of MCP at 1.6 Å resolution at BESSY Beamline BL14.1 using seleno-methionated and native protein. The monomer constitutes a Rossmann fold with two homodimers forming a symmetrical tetramer in solution (Fig. 1). Strikingly, all MCP monomers observed in two different crystal forms share a disordered surface loop (residues 70-76). Based on detailed analyses, including shape (Fig. 2A), charge distribution (Fig. 2B), and conservation (Fig. 2C), this region was proposed to represent the Moco-binding site. In silico docking studies, structural comparison as well as the identification of an anion binding site further supported this hypothesis. Finally, structure-guided mutagenesis in combination with substrate binding studies (Fig. 2D) confirmed this region as the Moco-binding site.

Reference

Ataya, F.S., Witte, C.P., Galvan, A., Igeno, M.I. and Fernandez, E. (2003) Mcp1 Encodes the Molybdenum Cofactor Carrier Protein in Chlamydomonas reinhardtii and Participates in Protection, Binding, and Storage Functions of the Cofactor. J. Biol. Chem., 278, 10885-10890

Witte, C.P., Igeno, M.I., Mendel, R., Schwarz, G. and Fernandez, E. (1998) The Chlamydomonas reinhardtii MoCo carrier protein is multimeric and stabilizes molybdopterin cofactor in a molybdate charged form. FEBS Lett., 431, 205-209.