TY - JOUR
T1 - Identification of the Ferredoxin-Binding Site of a Ferredoxin-Dependent Cyanobacterial Nitrate Reductase
AU - Srivastava, Anurag P.
AU - Hardy, Emily P.
AU - Allen, James
AU - Vaccaro, Brian J.
AU - Johnson, Michael K.
AU - Knaff, David B.
N1 - Funding Information:
*Telephone: 847-578-3458. Fax: 847-578-3240. E-mail: anurag. srivastava@rosalindfranklin.edu. ORCID Anurag P. Srivastava: 0000-0003-3493-1375 Present Address ⊥A.P.S.: Department of Biochemistry and Molecular Biology, Rosalind Franklin University of Medicine and Science, North Chicago, IL 60064. Funding The mutagenesis, protein expression and purification, kinetic measurements, and substrate binding determinations performed at Texas Tech University were funded by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy, through Grant DE-FG03-99ER20346 (to D.B.K.). The in silico structural modeling and the Fe and Mo determinations performed at Arizona State University were supported by National Science Foundation Grant CHE 1505874 (to J.P.A.). Funding for the EPR spectrometry and spin quantitation measurements was provided by the National Institutes of Health, through Grant GM62524 (to M.K.J.). Notes The authors declare no competing financial interest.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/10/17
Y1 - 2017/10/17
N2 - An in silico model for the 1:1 ferredoxin (Fd)/nitrate reductase (NR) complex, using the known structure of Synechocystis sp. PCC 6803 Fd and the in silico model of Synechococcus sp. PCC 7942 NR, is used to map the interaction sites that define the interface between Fd and NR. To test the electrostatic interactions predicted by the model complex, five positively charged NR amino acids (Arg43, Arg46, Arg197, Lys201, and Lys614) and a negatively charged amino acid (Glu219) were altered using site-directed mutagenesis and characterized by activity measurements, metal analysis, and electron paramagnetic resonance (EPR) studies. All of the charge replacement variants retained wild-type levels of activity with reduced methyl viologen (MV), but a significant decrease in activity was observed for the R43Q, R46Q, K201Q, and K614Q variants when reduced Fd served as the electron donor. EPR analysis as well as the Fe and Mo analyses showed that loss of activity observed with these variants was not the consequence of perturbation of the Mo center or [4Fe-4S] cluster. Therefore, the loss of the Fd-linked specific activity observed with these variants can be explained only by invoking a role for Arg43, Arg46, Lys201, and Lys614 in Fd binding. The R43Q, R46Q, K201Q, and K614Q NR variants also showed a decreased binding affinity for Fd, compared to that of wild-type NR, supporting a key role of these four positively charged residues in the productive binding of Fd.
AB - An in silico model for the 1:1 ferredoxin (Fd)/nitrate reductase (NR) complex, using the known structure of Synechocystis sp. PCC 6803 Fd and the in silico model of Synechococcus sp. PCC 7942 NR, is used to map the interaction sites that define the interface between Fd and NR. To test the electrostatic interactions predicted by the model complex, five positively charged NR amino acids (Arg43, Arg46, Arg197, Lys201, and Lys614) and a negatively charged amino acid (Glu219) were altered using site-directed mutagenesis and characterized by activity measurements, metal analysis, and electron paramagnetic resonance (EPR) studies. All of the charge replacement variants retained wild-type levels of activity with reduced methyl viologen (MV), but a significant decrease in activity was observed for the R43Q, R46Q, K201Q, and K614Q variants when reduced Fd served as the electron donor. EPR analysis as well as the Fe and Mo analyses showed that loss of activity observed with these variants was not the consequence of perturbation of the Mo center or [4Fe-4S] cluster. Therefore, the loss of the Fd-linked specific activity observed with these variants can be explained only by invoking a role for Arg43, Arg46, Lys201, and Lys614 in Fd binding. The R43Q, R46Q, K201Q, and K614Q NR variants also showed a decreased binding affinity for Fd, compared to that of wild-type NR, supporting a key role of these four positively charged residues in the productive binding of Fd.
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U2 - 10.1021/acs.biochem.7b00025
DO - 10.1021/acs.biochem.7b00025
M3 - Article
C2 - 28520412
AN - SCOPUS:85031674096
SN - 0006-2960
VL - 56
SP - 5582
EP - 5592
JO - Biochemistry
JF - Biochemistry
IS - 41
ER -