Homology modelling ?

1. Homology modelling ? NMR ? X-ray ?

2. Homology Modelling !

3. Helices are Helices

4. Strands are Strands

5. Structure=Conservation

6. Structure=Conservation

7. Modelling beats X-ray

8. Data ~ infinite…

9. What can be Modelled ?

10. What can be Modelled ?

11. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate

12. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate

13. Template detection Normally BLAST is good enough. If BLAST doesn’t find a template, You should not want to build a model. When desperate, use PSI-BLAST (on PDB + SwissProt), or use threading.

14. Threading Threading means: Use information from the template structure to detect homology, or to improve an alignment.

15. Threading Small residues

16. Threading Alcoholic residues

17. Threading The folded ‘protein’

18. Threading Two aligned ‘proteins’

19. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate

20. Alignment Run BLAST on model sequence Run BLAST on template sequence Select 50-100 representatives Do multiple sequence alignment Keep only model and template

21. How to align: ASASASASASAS YPYPYPYPYPYP (three ways…)

22. How to align: ASASASASASAS- AYAYAYAYAYAY- -YPYPYPYPYPYP (two ways…)

23. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate

24. Alignment optimization 1 Use threading techniques. 2 Shift gaps around:

25. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate

26. Select ‘best’ template

27. Deal with errors

28. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate

29. Exchange side chains Keep template rigid Determine best rotamer Do NOT optimize rotamers If best rotamer doesn’t fit, start thinking. If the model is bad, you had the wrong template, or the wrong alignment. Make sure your model exists…

30. Position specific rotamers

31. Position specific rotamers

32. Position specific rotamers

33. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate

34. Insertions - Deletions Insertions are impossible Deletions: Move gap around in template till end point distance is short. If this is not possible, you have either the wrong template, or the wrong alignment.

35. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate

36. Model Optimization Do NOT use molecular dynamics:

37. Model Optimization Use 25 – 50 steps energy minimization, or use a force field that has been especially designed for the optimization of homology models.

38. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate

39. The ‘8’ Steps of Modelling 1 Detect template 2 Get alignment 3 Optimize alignment 4 Optimize template 5 Exchange side chains 6 Deal with insertions/deletions 7 Optimize model 8 Validate 9 Iterate