Two sets of points are given: A = (a1, a2,… an) and B = (b1, b2,… bn) in 3D. The optimal part set of A(P) and B(Q) (absolute value) are searched. We try to find the optimal rigid body transformations (Gopt) between A(P) and B(Q) sets which gives the minimal distances (D) by the rigid body transformations..
To compare the structures there are some softwares: Dali [2], CE CALCULATOR [3], MATRAS [4], SSAP (CATH) [5], TIP-STRUCTFAST [6], SuperPose [7], VAST [8.] (see Table 7.4.)
If the sequence identity is less than 30%, our modells are unreliable, between 30-60% the modell is reliable, buti t has unreliable regions, at larger than 60% our modell is reliable. We have to be careful if homology modelling is near the binding pocket. Binding pocket is sensitive enough, we have to „positively believe” in our results and handle with critics.
Table 7.3. Some softwares to compare the protein structures
Name of the software
|
Input
|
Output
|
Dali [2]
|
pdb file/pdb code
|
structure fitting and alignment
|
Cath (SSAP) [5]
|
pdb file/pdb code
|
structure fitting and pairwise alignment
|
Ce calculator [3]
|
pdb file/pdb code
|
pdb file, structure alignment (Rasmol)
|
Matras [4]
|
pdb file/pdb code
|
structure fitting and pairwise alignment, pairwise 3D alignment
|
SuperPose [7]
|
pdb file/pdb code
|
sequence fitting and alignment (PDB), RMSD
|
The results of the homology modelling with different servers of BSA (Bovine Serum Albumine) from HSA (Human Serum Albumine) structure) are described in Figure 7.5.-Figure 7.10. As it can be seen the structures are similar after homology modelling but we can find differences int he positions of secondary structure. Table 7.5 includes the frequencies of aminoacids in BSA and HSA for modelling homology modelling. As it can be seen, the frequency of aminoacids is very similar between BSA and HSA.
Table 7.4. The frequency and the number of aminoacids in BSA and HSA
Aminosav
|
HSA
|
BSA
|
Aminosav
|
HSA
|
BSA
|
Alanin (A)
|
0,103
|
0,079
|
Alanin (A)
|
63
|
48
|
Cisztein (C)
|
0,057
|
0,058
|
Cisztein (C)
|
35
|
35
|
Aszparginsav (D)
|
0,069
|
0,066
|
Aszparginsav (D)
|
36
|
40
|
Glutaminsav (E)
|
0,102
|
0,097
|
Glutaminsav (E)
|
62
|
59
|
Fenilalanin (F)
|
0,057
|
0,049
|
Fenilalanin (F)
|
35
|
30
|
Glicin (G)
|
0,021
|
0,028
|
Glicin (G)
|
13
|
17
|
Hisztidin (H)
|
0,026
|
0,028
|
Hisztidin (H)
|
16
|
17
|
Izolucein (I)
|
0,015
|
0,025
|
Izolucein (I)
|
9
|
15
|
Lizin (K)
|
0,099
|
0,099
|
Lizin (K)
|
60
|
60
|
Leucin (L)
|
0,105
|
0,107
|
Leucin (L)
|
64
|
65
|
Metionin (M)
|
0,011
|
0,008
|
Metionin (M)
|
7
|
5
|
Aszpargin (N)
|
0,028
|
0,023
|
Aszpargin (N)
|
17
|
14
|
Prolin (P)
|
0,039
|
0,045
|
Prolin (P)
|
24
|
28
|
Glutamin (G)
|
0,033
|
0,033
|
Glutamin (G)
|
20
|
20
|
Arginin (R)
|
0,044
|
0,043
|
Arginin (R)
|
27
|
26
|
Szerin (S)
|
0,046
|
0,053
|
Szerin (S)
|
28
|
32
|
Treonin (T)
|
0,048
|
0,056
|
Treonin (T)
|
29
|
34
|
Valanin (V)
|
0,071
|
0,063
|
Valanin (V)
|
43
|
38
|
Triptofán (W)
|
0,003
|
0,005
|
Triptofán (W)
|
2
|
3
|
Tirozin (Y)
|
0,031
|
,0035
|
Tirozin (Y)
|
19
|
21
|
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