Part:BBa_K2740018

CR1 nifX

CR1 nifX encodes nitrogen fixation protein NifX that favors the insertion of molybdenum-iron protein cofactors into nitrogenase.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]

Parameter of Protein

Number of amino acids: 129

Molecular weight: 14126.33

Theoretical pI: 6.51

Amino acid composition:
Ala (A)  16  12.4%
Arg (R)   7    5.4%
Asn (N)   4   3.1%
Asp (D)   3   2.3%
Cys (C)   1    0.8%
Gln (Q)   7    5.4%
Glu (E)  11    8.5%
Gly (G)  10    7.8%
His (H)   5    3.9%
Ile (I)    10   7.8%
Leu (L)  10    7.8%
Lys (K)   6    4.7%
Met (M)  5     3.9%
Phe (F)   7     5.4%
Pro (P)   4     3.1%
Ser (S)   7     5.4%
Thr (T)   5     3.9%
Trp (W)  1     0.8%
Tyr (Y)   0    0.0%
Val (V)  10    7.8%
Pyl (O)   0     0.0%
Sec (U)   0    0.0%

 (B)   0         0.0%
(Z)   0   0.0%
(X)   0         0.0%

 

Total number of negatively charged residues (Asp + Glu): 14
Total number of positively charged residues (Arg + Lys): 13

Atomic composition:

Carbon      C           627
Hydrogen    H         1006
Nitrogen    N            178
Oxygen      O          181
Sulfur      S               6

Formula: C627H1006N178O181S6
Total number of atoms: 1998

Extinction coefficients:

Extinction coefficients are in units of  M-1 cm-1, at 280 nm measured in water.

Ext. coefficient     5500
Abs 0.1% (=1 g/l)   0.389, assuming all pairs of Cys residues form cystines

 

Ext. coefficient     5500
Abs 0.1% (=1 g/l)   0.389, assuming all Cys residues are reduced

Estimated half-life:

The N-terminal of the sequence considered is M (Met).

The estimated half-life is: 30 hours (mammalian reticulocytes, in vitro).
>20 hours (yeast, in vivo).
>10 hours (Escherichia coli, in vivo).

 

Instability index:

The instability index (II) is computed to be 47.67
This classifies the protein as unstable.

 

Aliphatic index: 95.35

Grand average of hydropathicity (GRAVY): 0.051

Design Notes

Nitrogenase is a complex enzyme system consisting of nine protein components. Additionally, to maintain stoichiometry of these protein components is an essential requirement for nitrogenase biosynthesis and activity. However, there is only one copy of each structure gene present in the nif gene cluster. Therefore, cloning each of these nif genes and setting as independent part can facilitate the regulation of balancing expression ratios from the transcription and/or translation level(s) when they are heterogeneously expressed in non-diazotrophic hosts.

Molecular modeling of nifX

To learn more about the molecular structure of nitrogen fixation protein NifX that favors the insertion of molybdenum-iron protein cofactors into nitrogenase encoded by nifX, we use Swiss-Model to get the molecular model.

Confirmation of Expression of nifX

We test expression profiles of each structure gene in the nif cluster that overexpressed in EJNC by conducting Real-time Quantitative PCR(qPCR). Relative expression compared to the housekeeping gene 16S rRNA is shown.

qRT-PCR analysis demonstrates that all the component genes of the nif cluster are significantly over expressed in EJNC whereas the transcription of these genes are no detected (N.D.) in nondiazotrophic E.coli JM109. Based on these analysis, we know nifx has a relatively low expression level.

Usage

In our this year’s project, we intends to establish a sound and ideal whole-cell photocatalytic nitrogen fixation system. We use the engineered E. coli cells to express nitrogenase and in-situ synthesize of CdS semiconductors in the biohybrid system. Instead of ATP-hydrolysis, such system is able to photocatalytic N2(nitrogen) to NH3(ammonia). The biohybrid system based on engineered E. coli cells with biosynthesis inorganic materials will likely become an alternative approach for the convenient utilization of solar energy. So, certainly we need not only a powerful solar power transition system but also a strong nitrogen fixation system to improve the efficiency of our whole-cell photocatalytic nitrogen fixation system. According to the above requirements, we choose a different nif gene cluster from Paenibacillus polymyxa CR1 to test its expression level.