TY - JOUR
T1 - Modeled ligand-protein complexes elucidate the origin of substrate specificity and provide insight into catalytic mechanisms of phenylalanine hydroxylase and tyrosine hydroxylase
AU - Maaß, Astrid
AU - Scholz, Joachim
AU - Moser, Andreas
PY - 2003/3/1
Y1 - 2003/3/1
N2 - NMR spectroscopy and X-ray crystallography have provided important insight into structural features of phenylalanine hydroxylase (PAH) and tyrosine hydroxylase (TH). Nevertheless, significant problems such as the substrate specificity of PAH and the different susceptibility of TH to feedback inhibition by L-3,4-dihydroxyphenylalanine (L-DOPA) compared with dopamine (DA) remain unresolved. Based on the crystal structures 5pah for PAH and 2toh for TH (Protein Data Bank), we have used molecular docking to model the binding of 6(R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) and the substrates phenylalanine and tyrosine to the catalytic domains of PAH and TH. The amino acid substrates were placed in positions common to both enzymes. The productive position of tyrosine in TH·BH4 was stabilized by a hydrogen bond with BH4. Despite favorable energy scores, tyrosine in a position trans to PAH residue His290 or TH residue His336 interferes with the access of the essential cofactor dioxygen to the catalytic center, thereby blocking the enzymatic reaction. DA and L-DOPA were directly coordinated to the active site iron via the hydroxyl residues of their catechol groups. Two alternative conformations, rotated 180° around an imaginary iron-catecholamine axis, were found for DA and L-DOPA in PAH and for DA in TH. Electrostatic forces play a key role in hindering the bidentate binding of the immediate reaction product L-DOPA to TH, thereby saving the enzyme from direct feedback inhibition.
AB - NMR spectroscopy and X-ray crystallography have provided important insight into structural features of phenylalanine hydroxylase (PAH) and tyrosine hydroxylase (TH). Nevertheless, significant problems such as the substrate specificity of PAH and the different susceptibility of TH to feedback inhibition by L-3,4-dihydroxyphenylalanine (L-DOPA) compared with dopamine (DA) remain unresolved. Based on the crystal structures 5pah for PAH and 2toh for TH (Protein Data Bank), we have used molecular docking to model the binding of 6(R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) and the substrates phenylalanine and tyrosine to the catalytic domains of PAH and TH. The amino acid substrates were placed in positions common to both enzymes. The productive position of tyrosine in TH·BH4 was stabilized by a hydrogen bond with BH4. Despite favorable energy scores, tyrosine in a position trans to PAH residue His290 or TH residue His336 interferes with the access of the essential cofactor dioxygen to the catalytic center, thereby blocking the enzymatic reaction. DA and L-DOPA were directly coordinated to the active site iron via the hydroxyl residues of their catechol groups. Two alternative conformations, rotated 180° around an imaginary iron-catecholamine axis, were found for DA and L-DOPA in PAH and for DA in TH. Electrostatic forces play a key role in hindering the bidentate binding of the immediate reaction product L-DOPA to TH, thereby saving the enzyme from direct feedback inhibition.
UR - http://www.scopus.com/inward/record.url?scp=0037351143&partnerID=8YFLogxK
U2 - 10.1046/j.1432-1033.2003.03429.x
DO - 10.1046/j.1432-1033.2003.03429.x
M3 - Journal articles
C2 - 12631267
AN - SCOPUS:0037351143
SN - 0014-2956
VL - 270
SP - 1065
EP - 1075
JO - European Journal of Biochemistry
JF - European Journal of Biochemistry
IS - 6
ER -