1. Introduction

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Takahashi, et al. studied the sequence characteristics of the urinary prokallikrein in 1988, they tended to think that the human urinary prokallikrein and kallikrein are of tissue type and they are excreted in urine without any modification [1]. Irie, et al. studied the reactivities of human urinary prokallikrein toward rabbit antibodies [2]. Kamada, et al. explored the tissue prokallikrein activation by some serine proteases in rat [3]. Binding of tissue prokallikrein to isolated human neutrophils was studied by some people twenty years before [4]. Other questions such as the correlation of two different assays for urinary kallikrein [5],the activation of urinary kallikrein in patients with interstitial cystitis [6], urinary kallikrein and salt sensitivity in essential hypertensive males [7], and so on [8-12] were studied by many people too, some works pointed out that there may be some relations between kidney cortex and urinary kallikrein [13,14]. In this paper, we explore the sequence characteristics of urinary kallikrein via some bioinformatics tools.

2. Materials And Methods

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In order to study the urinary prokallikrein from the bioinformatics perspective, the sequences data is downloaded from National Center for Biotechnology Information (NCBI) (accession number: 1409287A). Chemical and physical properties are predicted by ProtParam tool (http://web.expasy.org/protparam/) [15]. The secondary structure of urinary prokallikrein is predicted via the SOPMA tool[16]. Then, the phosphorylation sites and the protein-protein interaction of urinary prokallikrein are respectively studied by the netphos tool and the STRING system [17]. The hydrophobicity of urinary prokallikrein is analyzed by the protscale system [18].

3. Results And Discussion

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Physical and chemical properties of urinary prokallikrein are studied by protparam system (Table 1). Physical and chemical properties for urinary prokallikrein prediction results show that there are 238 amino acids with the molecular weight is 26405.55. Total number of atoms is 3619, and instability index is 37.98.

Table 1

Hydrophobicity is determined by the amino acids sequences. The Hydrophobicity map of urinary prokallikrein sequences is calculated by the Hphoh. / Kyte & Doolittle scale in ExPASy's ProtScale program and the result is shown in Fig.1. In the Fig.1, while vertical value above 0 denotes the hydrophobic area. And it is easily can be seen that there are more hydrophilic residues than the hydrophobic residues in urinary prokallikrein.

The most common secondary structure is the α-helix, β-fold, turn and random coil. The secondary structure of urinary prokallikrein is predicted via SOPMA system, and the prediction result is shown in Fig.2. The result shows that there are 57(23.95%) alpha helix, 60(25.21%) beta sheet, 31(13.03%) turn and 90(37.82%) coil in the urinary prokallikrein sequence.

Figure 1    Figure 2

The main sites for protein phosphorylation are serine, threonine and tyrosine. These sites for phosphorylation in urinary prokallikrein are studied via the NetPhos system, and the result is shown in the Fig.3. There are 8 serine phosphorylation sites (potential value higher than 0.5), 5 threonine phosphorylation sites (potential value higher than 0.5), and 3 tyrosine are phosphorylation sites (potential value higher than 0.5) in the urinary prokallikrein.

Protein-protein interaction characteristics of urinary prokallikrein is predicted via String online system, and the results is shown in the Fig.4. The results show that there are 11 nodes in the protein-protein interaction network, and there are 29 interaction edges with the average node degree 5.27, PPI enrichment p-value: 0.000146.

The structural characteristics of urinary prokallikrein have not attracted many scientists, so, there is very few related works. In our study, some important characteristics of urinary prokallikrein are predicted via some famous prediction tools, and all of these tools are all widely used in studying the structure of proteins.

Figure 3    Figure 4

4. Conclusion

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Although protein techniques can be used for obtaining protein expression data, the bioinformatics tools may be used to verify this data. It is important to investigate information contained in urinary prokallikrein. In this paper,sequence characteristics, such as basic physical and chemical properties, phosphorylation sites, protein-protein interaction network of urinary prokallikrein are predicted via some bioinformatics tools.

Acknowledgments

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This research work was supported by president fund of Xi’an Technological University (No.XA GDXJJ14011).

References

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