Genetic Complementation Studies of Human Pin1 in Azotobacter vinelandii Revealed that it Requires Amino Terminus of the NifM to Deliver PPIase Effect to the Fe-protein of Nitrogenase

The NifM is a peptidyl prolyl cis-trans isomerase and is required for the maturation and activation of the Fe protein of Nitrogenase. Since the carboxyl terminus of NifM is similar to the Human Pin1, we expressed the Human Pin1 in A. vinelandii BG98, a nifM mutant strain containing a kanamycin insertion and found that it could not complement the function of nifM. It was hypothesized that the amino terminus of the NifM might be required for the Pin1 to bind to NifH similar to requirement of the WW domain for the binding to pSer/Thr-Pro of Cdc25C. Therefore we expressed a NifM amino-terminal and Pin1 fusion protein chimera in A. vinelandii BG98 and this chimera was able to complement the function of NifM. This observation indicated that the amino-terminal of NifM is responsible for the specificity for NifH similar to the specificity of WW domain of Pin1 for pSer/Thr-Pro while the carboxyl terminal domain functions as peptidyl prolyl cis/trans isomerase.