Insight into structural rearrangements and interdomain interactions related to electron transfer between flavin mononucleotide and heme in nitric oxide synthase: A molecular dynamics study.
Calmodulin (CaM) binding to nitric oxide synthase (NOS) enables a conformational change, in which the FMN domain shuttles between the FAD and heme domains to deliver electrons to the active site heme center. A clear understanding of this large conformational change is critical, since this step is the rate-limiting in NOS catalysis. Herein molecular dynamics simulations were conducted on a model of an oxygenase/FMN (oxyFMN) construct of human inducible NOS (iNOS). This is to investigate the structural rearrangements and the domain interactions related to the FMN-heme interdomain electron transfer (IET). We carried out simulations on the iNOS oxyFMN·CaM complex models in [Fe(III)][FMNH(-)] and [Fe(II)][FMNH] oxidation states, the pre- and post-IET states. The comparison of the dynamics and conformations of the iNOS construct at the two oxidation states has allowed us to identify key factors related to facilitating the FMN-heme IET process. The computational results demonstrated, for the first time, that the conformational change is redox-dependent. Predictions of the key interacting sites in optimal interdomain FMN/heme docking are well supported by experimental data in the literature. An intra-subunit pivot region is predicted to modulate the FMN domain motion and correlate with existence of a bottleneck in the conformational sampling that leads to the electron transfer-competent state. Interactions of the residues identified in this work are proposed to ensure that the FMN domain moves with appropriate degrees of freedom and docks to proper positions at the heme domain, resulting in efficient IET and nitric oxide production.
Department of Chemistry & Physics, College of Arts & Sciences, Florida Gulf Coast University, 10501 FGCU Blvd. S., Fort Myers, FL 33965, USA. Electronic address: ysheng@fgcu.edu.
Yinghong
Y
Sheng
Pennsylvania State University at Mont Alto, 1 Campus Drive, Mont Alto, PA 17237, USA.
Linghao
L
Zhong
Department of Bioengineering and Software Engineering, U.A. Whitaker College of Engineering, Florida Gulf Coast University, 10501 FGCU Blvd. S., Fort Myers, FL 33965, USA.
Dahai
D
Guo
Department of Chemistry & Physics, College of Arts & Sciences, Florida Gulf Coast University, 10501 FGCU Blvd. S., Fort Myers, FL 33965, USA.
Gavin
G
Lau
Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA. Electronic address: cfeng@unm.edu.
Changjian
C
Feng
D002147:Calmodulin / Q000737:chemistry*; D005486:Flavin Mononucleotide / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006801:Humans; D007501:Iron / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D052247:Nitric Oxide Synthase Type II / Q000737:chemistry*; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary
D002147:Calmodulin; D006418:Heme; D005486:Flavin Mononucleotide; D007501:Iron; D052247:Nitric Oxide Synthase Type II
Calmodulin; Electron transfer; Heme; Molecular dynamics; Nitric oxide synthase