title: Negative cooperativity in the nitrogenase Fe protein electron delivery cycle.
abstract: Nitrogenase catalyzes the ATP-dependent reduction of dinitrogen (N2) to two ammonia (NH3) molecules through the participation of its two protein components, the MoFe and Fe proteins. Electron transfer (ET) from the Fe protein to the catalytic MoFe protein involves a series of synchronized events requiring the transient association of one Fe protein with each αβ half of the α2β2MoFe protein. This process is referred to as the Fe protein cycle and includes binding of two ATP to an Fe protein, association of an Fe protein with the MoFe protein, ET from the Fe protein to the MoFe protein, hydrolysis of the two ATP to two ADP and two Pifor each ET, Pirelease, and dissociation of oxidized Fe protein-(ADP)2from the MoFe protein. Because the MoFe protein tetramer has two separate αβ active units, it participates in two distinct Fe protein cycles. Quantitative kinetic measurements of ET, ATP hydrolysis, and Pirelease during the presteady-state phase of electron delivery demonstrate that the two halves of the ternary complex between the MoFe protein and two reduced Fe protein-(ATP)2do not undergo the Fe protein cycle independently. Instead, the data are globally fit with a two-branch negative-cooperativity kinetic model in which ET in one-half of the complex partially suppresses this process in the other. A possible mechanism for communication between the two halves of the nitrogenase complex is suggested by normal-mode calculations showing correlated and anticorrelated motions between the two halves.
authors.affiliation: Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322.
authors.forename: Karamatullah
authors.initials: K
authors.lastname: Danyal
authors.affiliation: Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322.
authors.forename: Sudipta
authors.initials: S
authors.lastname: Shaw
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, IL 60208.
authors.forename: Taylor R
authors.initials: TR
authors.lastname: Page
authors.affiliation: Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322.
authors.forename: Simon
authors.initials: S
authors.lastname: Duval
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, IL 60208.
authors.forename: Masaki
authors.initials: M
authors.lastname: Horitani
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, IL 60208.
authors.forename: Amy R
authors.initials: AR
authors.lastname: Marts
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, IL 60208.
authors.forename: Dmitriy
authors.initials: D
authors.lastname: Lukoyanov
authors.affiliation: Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Dean
authors.affiliation: Catalysis Science, Physical Science Division, Pacific Northwestern National Laboratory, Richland, WA 99352.
authors.forename: Simone
authors.initials: S
authors.lastname: Raugei
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, IL 60208; bmh@northwestern.edu lance.seefeldt@usu.edu edwin.antony@marquette.edu.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hoffman
authors.affiliation: Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322; bmh@northwestern.edu lance.seefeldt@usu.edu edwin.antony@marquette.edu.
authors.forename: Lance C
authors.initials: LC
authors.lastname: Seefeldt
authors.affiliation: Department of Biological Sciences, Marquette University, Milwaukee, WI 53201 bmh@northwestern.edu lance.seefeldt@usu.edu edwin.antony@marquette.edu.
authors.forename: Edwin
authors.initials: E
authors.lastname: Antony
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D004579:Electron Transport; D006868:Hydrolysis; D007700:Kinetics; D008983:Molybdoferredoxin / Q000737:chemistry* / Q000378:metabolism; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism; D009586:Nitrogen Fixation; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D012474:Salmon / Q000378:metabolism
chemical_list: D008983:Molybdoferredoxin; D046912:Multiprotein Complexes; D000255:Adenosine Triphosphate; D010088:Oxidoreductases; C029130:nitrogenase reductase
keywords: ATP hydrolysis; allosteric control; conformational control; half-sites reactivity