Structural Insights into the Incorporation of the Mo Cofactor into Sulfite Oxidase from Site-Directed Spin Labeling.
Mononuclear molybdoenzymes catalyze a broad range of redox reactions and are highly conserved in all kingdoms of life. This study addresses the question of how the Mo cofactor (Moco) is incorporated into the apo form of human sulfite oxidase (hSO) by using site-directed spin labeling to determine intramolecular distances in the nanometer range. Comparative measurements of the holo and apo forms of hSO enabled the localization of the corresponding structural changes, which are localized to a short loop (residues 263-273) of the Moco-containing domain. A flap-like movement of the loop provides access to the Moco binding-pocket in the apo form of the protein and explains the earlier studies on the in vitro reconstitution of apo-hSO with Moco. Remarkably, the loop motif can be found in a variety of structurally similar molybdoenzymes among various organisms, thus suggesting a common mechanism of Moco incorporation.
Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin (Germany).
Aaron
A
Hahn
Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany).
Christopher
C
Engelhard
Institut für Biochemie und Biologie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Golm (Germany).
Stefan
S
Reschke
Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany).|Berlin Joint EPR Laboratory Freie Universität Berlin (Germany).
Christian
C
Teutloff
Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany).|Berlin Joint EPR Laboratory Freie Universität Berlin (Germany).
Robert
R
Bittl
Institut für Biochemie und Biologie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Golm (Germany).
Silke
S
Leimkühler
Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin (Germany). risse@chemie.fu-berlin.de.|Berlin Joint EPR Laboratory Freie Universität Berlin (Germany). risse@chemie.fu-berlin.de.
Thomas
T
Risse
EPR spectroscopy; biocatalysis; cofactors; enzymes; protein structures