The Nitrogenase FeMo-Cofactor Precursor Formed by NifB Protein: A Diamagnetic Cluster Containing Eight Iron Atoms.
The biological activation of N2 occurs at the FeMo-cofactor, a 7Fe-9S-Mo-C-homocitrate cluster. FeMo-cofactor formation involves assembly of a Fe6-8 -SX -C core precursor, NifB-co, which occurs on the NifB protein. Characterization of NifB-co in NifB is complicated by the dynamic nature of the assembly process and the presence of a permanent [4Fe-4S] cluster associated with the radical SAM chemistry for generating the central carbide. We have used the physiological carrier protein, NifX, which has been proposed to bind NifB-co and deliver it to the NifEN protein, upon which FeMo-cofactor assembly is ultimately completed. Preparation of NifX in a fully NifB-co-loaded form provided an opportunity for Mössbauer analysis of NifB-co. The results indicate that NifB-co is a diamagnetic (S=0) 8-Fe cluster, containing two spectroscopically distinct Fe sites that appear in a 3:1 ratio. DFT analysis of the (57) Fe electric hyperfine interactions deduced from the Mössbauer analysis suggests that NifB-co is either a 4Fe(2+) -4Fe(3+) or 6Fe(2+) -2Fe(3+) cluster having valence-delocalized states.
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Ave, Pittsburgh, PA, 15213, USA. ysguo@andrew.cmu.edu.
Yisong
0000-0002-4132-3565
Y
Guo
Centro de Biotecnología y Genómica de Plantas, Universidad Politénica de Madrid (UPM)-, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Campus Montegancedo UPM, 28223-Pozuelo de Alarcón, Madrid, Spain.
Carlos
0000-0001-8363-5199
C
Echavarri-Erasun
Centro de Biotecnología y Genómica de Plantas, Universidad Politénica de Madrid (UPM)-, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Campus Montegancedo UPM, 28223-Pozuelo de Alarcón, Madrid, Spain.
Marie
0000-0002-8702-1001
M
Demuez
Centro de Biotecnología y Genómica de Plantas, Universidad Politénica de Madrid (UPM)-, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Campus Montegancedo UPM, 28223-Pozuelo de Alarcón, Madrid, Spain.
Emilio
E
Jiménez-Vicente
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Ave, Pittsburgh, PA, 15213, USA. eb7g@andrew.cmu.edu.
Emile L
EL
Bominaar
Centro de Biotecnología y Genómica de Plantas, Universidad Politénica de Madrid (UPM)-, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Campus Montegancedo UPM, 28223-Pozuelo de Alarcón, Madrid, Spain. lm.rubio@upm.es.
Luis M
0000-0003-1596-2475
LM
Rubio
D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D058085:Iron Compounds / Q000737:chemistry / Q000378:metabolism*; D060526:Magnetic Fields; D008983:Molybdoferredoxin / Q000737:chemistry / Q000378:metabolism*; D009591:Nitrogenase / Q000737:chemistry / Q000378:metabolism*; D011789:Quantum Theory
D058085:Iron Compounds; D008983:Molybdoferredoxin; C085381:NifB cofactor; D007501:Iron; D009591:Nitrogenase
biosynthesis; iron-molybdenum cofactors; metalloproteins; mössbauer spectroscopy; nitrogenases