Results
Protein engineering of a tetra-arginine cluster based endotheolial NOS
We hypothesized that substituting the cysteines that formed ZnS4 cluster with arginines would still form an active eNOS homodimer, but one that was redox insensitive. Molecular dynamic (MD) experiments were initially undertaken using the available crystal structure of human eNOS (PDB ID 3NOS) to determine if mutations of the two tetrathiolate clusters generating cysteine residues to arginines (C94R/C99R) would grossly alter the eNOS structure. A phosphate ion (PO3-4) was introduced as a replacement for the Zn2+ ion. The resulting mutant protein was simulated in a water filled cube for 100 ns using the MD simulation module in Yasara. After minimization of free energy, the structure of eNOS was still predicted to be dimeric and three arginine residues were found to interact with the phosphate ion. Four arginines failed to form a compact tetrahedral structure, however, the structure of catalytic center and substrate channel did not appear to be disturbed in the C94R/C99R mutant eNOS.