Abstract
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.
Highlights
Nitrogenase, the enzyme responsible for conversion of atmospheric nitrogen to ammonia, consists of two separable protein components the Fe protein and the MoFe protein, both of which are extremely oxygen-sensitive [1,2,3]
Human Pin1 Protein does not complement the NifM function in A. vinelandii: Sequence comparison of Human Pin1 and the NifM of A. vinelandii revealed that the peptidyl prolyl cis-trans isomerase domain of the Human Pin1 is similar to the peptidyl prolyl cis-trans isomerase domain of NifM and this sequence similarity is confined to the carboxyl terminus of NifM (Fig.1)
The A. vinelandii BG3302 over expresses the Pin1 protein under nitrogen limiting conditions as it is under the control of the nifH promoter, and if the peptidyl prolyl isomerase activity of the Pin1 protein is sufficient to take up the function of the NifM protein it should lead to the activation and stabilization of the NifH of the nitrogenase leading to a Nif+ phenotype of the strain
Summary
Nitrogenase, the enzyme responsible for conversion of atmospheric nitrogen to ammonia, consists of two separable protein components the Fe protein and the MoFe protein, both of which are extremely oxygen-sensitive [1,2,3]. In A. vinelandii, the nifU and nifS together with the nifM gene product are required for full stability and activation of the Fe protein [12, 13].
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