Why do Comparative Modelling?

• X-ray crystallography is a time-consuming process requiring expensive equipment.
• In some (now relatively rare) cases, proteins simply cannot be purified in sufficient quantities and crystallized.
• The volume of sequence data (which is now fast and easy to obtain) far outstrips structural data.
• The volume of sequence and structure data is doubling approximately every 18 months.

The PDB Contains:

11,800 x-ray crystal structures
~2,200 NMR structures
~9,000 distinct sequences (many structures are of the same protein)

The GenBank Sequence Databank Contains:

~10,000,000 sequences