Homology ModelingHomology Modeling

Seminar produced by Hanka Venselaar

Homology modeling

# residues

% id

entit

y

*

* Actually, modelling is possible here, but we cannot get an alignment…

Yes we can

Homology modeling in short…Prediction of structure based upon a highly similar structure

Add sidechains, Molecular Dynamics simulation on model

Unknown structure

NSDSECPLSHDG

NSDSECPLSHDG

|| || | ||

NSYPGCPSSYDG

Alignment of model and template sequence

Known structure

Known structure Back bone copiedCopy backbone and conserved residues

Model!

The 8 steps of Homology modeling

1: Template recognition and initial alignment

1: Template recognition and initial alignment

• BLAST your sequence against PDB

• Best hit normally template

1: Template recognition and initial alignment

2: Alignment correction

2: Alignment correction

• Functional residues conserved• Use multiple sequence alignments• Deletions shift gaps

CPISRTGASIFRCW CPISRTGASIFRCWCPISRTA---FRCW CPISRT---AFRCW

CPISRTAAS-FRCWCPISRTG-SMFRCWCPISRTA--TFRCWCPISRTAASHFRCWCPISRTGASIFRCW CPISRTA---FRCW

Both are possible

Multipe sequence alignment

Correct alignment

Sequence with known structure

Your sequence

2: Alignment correction

• Core residues conserved• Use multiple sequence alignments• Deletions in your sequence shift gaps

Known structure FDICRLPGSAEAV

Model FNVCRMP---EAI

Model FNVCR---MPEAI

S

G

P

L

A

E

R

C

I V

C

R

M

P

EV

C

R M

P

E

Correct alignment

F-D--A-V

1: Template recognition and initial alignment

2: Alignment correction

3: Backbone generation

3: Backbone generation

• Making the model….• Copy backbone of template to model• Make deletions as discussed• (Keep conserved residues)

1: Template recognition and initial alignment

2: Alignment correction

3: Backbone generation

4: Loop modeling

4: Loop modeling

Known structure GVCMYIEA---LDKYACNC

Your sequence GECFMVKDLSNPSRYLCKC

Loop library,

try different options

1: Template recognition and initial alignment

2: Alignment correction

3: Backbone generation

4: Loop modeling

5: Sidechain modeling

5: Side-chain modeling

• Several options• Libraries of preferred rotamers based

upon backbone conformation

1: Template recognition and initial alignment

2: Alignment correction

3: Backbone generation

4: Loop modeling

5: Sidechain modeling

6: Model optimization

6: Model optimization

• Molecular dynamics simulation• Remove big errors

• Structure moves to lowest energy conformation*

* Which has nothing to do with the real coordinates...

1: Template recognition and initial alignment

2: Alignment correction

3: Backbone generation

4: Loop modeling

5: Sidechain modeling

6: Model optimization

7: Model validation

7: Model Validation

• Second opinion by PDBreport /WHAT IF• Errors in active site? new alignment/

template

• No errors? Model!

1: Template recognition and initial alignment

2: Alignment correction

3: Backbone generation

4: Loop modeling

5: Sidechain modeling

6: Model optimization

7: Model validation

8: Iteration8: Iteration

8: Iteration

8: Iteration

Model!

1: Template recognition and initial alignment

2: Alignment correction

3: Backbone generation

4: Loop modeling

5: Sidechain modeling

6: Model optimization

7: Model validation

8: Iteration8: Iteration

8: Iteration

8: Iteration

8 steps of homology modeling1: Template recognition and initial alignment2: Alignment correction3: Backbone generation4: Loop modeling5: Side-chain modeling6: Model optimization7: Model validation8: Iteration

Alignment

Modeling

Correction