Cyprinus carpio Hsp70 protein is one important protein which not only helps in the protection from thermal stress but also act as marker in different malignant melanoma such as renal cell carcinoma
(Ramp et al., 2007). So detail information regarding physiochemical and structural characteristics of Hsp70 is needed for the functional annotation and for the well management of common carp fish at the farmer level.
Cyprinus carpio Hsp70 protein sequence
The lengths of the retrieved Hsp70 protein (Uniport Id: G3LU45) showed 643 number of amino acid (Table 1), but there was no crystal structure available in the Uniport protein database, which can be predicted through homology modeling from its amino acids sequence. This protein showed three conserved domains, present in 11-18, 199-212 and 336-350 amino acid region but the status of the protein showed unreviewed
(Zhang et al., 2011). That means this protein needs to be physiochemically and structurally characterized thoroughly for further understanding of it functions at the molecular level.
Physicochemical characteristics
In this study, the physiochemical parameters were estimated upon ExPasy ProtParam tool and were shown in Table 2. The result suggested that the average molecular weight and the theoretical pI of
Cyprinus carpio Hsp70 protein is 70kDa and 5.47 respectively which can be inferred that it is an acidic protein as acidic amino acids such as aspartic acid and glutamic acid are occurred 12% more abundance than the basic amino acids (
Kozlowski, 2017). The instability index was found 35.24 which suggests this protein is more stable in nature which may be due presence of large number of various molecular interactions including hydrogen, hydrophobic, electrostatic as well as Vander wall force of attraction
(Deller et al., 2016). In this study, the aliphatic index was found 82.83 which indicate that this protein is thermally stable. This is due to large number of hydrophobic interactions which may be inferred that significant number of aliphatic side chain amino acids such as alanine, valine, isoleucine and leucine makes the internal core of this protein (
Bischof and He, 2005). Further, the grand average hydropathy (GRAVY) was found -0.419 which indicates that the Hsp70 protein is more hydrophilic in nature which may be due presence of large number of hydrogen bonds in the protein.
(Xi et al., 2017). This study also suggested that it is a nuclear protein which might be induced in nucleus during environmental stress
(Sampuda et al., 2017). Moreover, no major peaks were found in the hydropathy plot during ProtoScale analysis shown in Fig 1 indicating the protein is more hydrophilic in nature (
Kyte and Doolittle, 1982).
Structural analysis
The analysis of secondary structure of
Cyprinus carpio Hsp70 predicted that there is more abundance of α helix (43.86%), extended strand (16.02%) and Random coil (40.12%) in the protein shown in Table 3 which can be inferred that this protein is very stable in nature. It might be due to extensive intra strand hydrogen bonding by the side chain of the amino acids
(Fujiwara et al., 2012) and the three conserved domains have been identified upon ProSite shown in Fig 2 which are at 11-18, 199-212, 336-350 amino acid length. It may be due to the protein has conserved and plays in similar function across species
(Shennan et al., 2020).
Homology modeling
As there is no avaibility of crystal structure for
Cyprinus carpio, Hsp70, Modeller 9.21, Phyre 2 and Swiss model were used for prediction of protein models. Our study revealed that the
bos tautus (PDB ID: 1YUW) has been solved to a resolution of 2.6 Å and chosen as the template for Modeller version 9.21. Further the alignment of the amino acid sequences of the Hsp70 protein from
Cyprinus carpio (UniProtKB ID: G3LU45) and
bos taurus (PDB ID: 1YUW) resulted identity of 89.87% which might be due presence of conserved amino acids which mediate common function in both of species
(Jiang et al., 2005).
The Modeller 9.21 resulted ten protein models with different discrete optimized protein energy (DOPE) shown in Table 4. The model structure such as target. B99990002 .pdb shown in (Fig 3A) with the lowest DOPE score (- 59973. 63672 Kcal/mol) was assessed and subsequently used for further analyses as protein attains the lowest free energy during the native state
(Rath et al., 2016). Further, the structural superimposition of
, Hsp70 of
Cyprinus carpio model with
bos tautus (chain A) both before and after energy minimization (Fig 3B) revealed a root mean square deviation (RMSD) score of 0.108 Å indicating that the structures were closely related (
Kufareva and Abagyan, 2012).
Phyre 2 was used to predict the
Cyprinus carpio Hsp70 protein by single highest scoring template
i.e. heat shock protein homolog sse1 (Chain C) (PDB ID: C3D2F) with 100% confidence and 88% identity shown in Fig 4A
(Basyuni et al., 2018). The result of Swiss modeling suggested that the generated model exist in oligomer state with no ligand showed in Fig 4B which may be due to presence of non enzymatic activity in the core of the protein
(Schwede et al., 2003). The QMEAN and GMQE score was found -1.57 and 0.80 indicating that the model is accurate and showed good degree of nativeness
(Sahoo et al., 2019). The BLAST result showed 89.87%, 57% of identity and similarity with template heat shock cognate 71 kDa protein (PDB ID: 1yuw.1.A) with resolution 2.60Å under X-ray. So it can be interfered that this two proteins are conserved across the species
(Cheeseman et al., 2016).
Comparative quality evaluation of the generated protein models
In this study, the quality of the above generated
Cyprinus carpio Hsp70 protein model by three above methods, were evaluated through different
Insilco platforms and the parameters are given in Table 5. The Ramachandran plot gives the shifting of residues in the mutant structure towards the disallowed region due to mutation as compared to native counterpart
(Pradhan et al., 2017). In this study, the analysis showed 94.2%, 93.8% and 92.7% of total amino acid residues lied in the favorable region of Modeller, Phyre 2 and Swiss models respectively shown in Fig 5 suggests that the protein model predicted from Modeller is more stable than the other two which may be due to absence of the methylene group at Cβ position of the amino acid residue indicating more number of glycine residues in allowed region (
Chakrabarti and Pal, 2001).
Further the ProSA-web analysis of the generated protein models revealed a Z score of -9.58, -9.48 and -10.93 (Fig 6) indicating Z value of all three falls in the middle of the graph suggesting all three models are of good quality and It may be due to the generated protein models have the conformations within the native experimental state (
Wiederstein and Sippl, 2007).
The ProQ analysis of above three generated
Cyprinus carpio Hsp70 models resulted Levitt-Gerstein (LG) and Maxsub score of (3.71, 0.35), (4.72, 0.435) and (4.972, 0.419) respectively, interfering that the protein model created by Modeler is of good and other two models generated by phyre 2 and Swiss modeling are of extremely good in quality. It might be due to correct optimization of the models to find their nativeness (
Olejniczak and Storz, 2017).
In this study, Verify3D plot analysis of all three modelled protein (Fig 7) remarked as PASS and the 3D environment profile resulted 80.87%, 83.93% and 90.96% of the residues have averaged 3D-1D score ≥*0.2, which suggests the Swiss modelled protein is structurally more valid than other two, it may be due to more compatibility of the Swiss model in respect to their location and environment of α, β, loop, polar as well as non polar structure
(Eisenberg et al., 1997).
Further the ERRAT analysis resulted that the overall quality values for all three Hsp70 models of
Cyprinus carpio were 82.56, 59.43 and 95.27 (Fig 8), suggesting that the overall quality of the generated model from Swiss modeling is highest followed by model generated by modeller and the value was lowest in the model structure predicted by Phyre 2. It might be due less randomized distributions of the different atom types and non bonded atomic interactions in Swiss model than the other two models (
Colovos and Yeates, 1993).