Apo-DHFR</scene> free of any of its ligands is displayed here.
Structure
E.coli DHFR is a small 159 amino acid protein approximately 18kDa. It has an a/b structure with eight central B strands and four helices. The protein can be thought to be made up of two subdomains, divided by the active site cleft. The which consists of residues 38-88 and the major subdomain comprised of about 100 residues. Three loops can be found in the major subdomain and they make up about 50% of this domain. They are the (residues 9-24), the (residues 116-132)and the (residues 142-150). The Met20 loop assumes different conformations during catalysis and accomodation of ligands is made possible by the 'hinge bending' motion about Lys 38 and Val 88 of the Adenosine binding domain.
Catalysis
DHFR catalyzes the reduction of 7,8-dihydrofolate to 5,6,7,8-tetrahydrofolate using reduced Nicotinamide Adenine Dinucleotide Phosphate (NADPH). This system has been key model to decipher enzyme catalysis and the intermediates of the catalytic cycle have been identified by crystallography. CPMG relaxation NMR experiments have also revealed that intermediates in the catalytic cycle exist in equilibrium with the preceding or following intermediate. Thus the binding of ligands seems to happen via a conformational selection rather than the traditional view of induced fit which is used to explain conformation change on ligand binding.
Drug Target
metho and trimetho [1].
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PDB structures
2cbr - hCRABP I – human
1cbr - CRABP I + retinoic acid – mouse
References
