TY - JOUR
T1 - HYSCORE Analysis of the Effects of Substrates on Coordination of Water to the Active Site Iron in Tyrosine Hydroxylase
AU - McCracken, John
AU - Eser, Bekir E.
AU - Mannikko, Donald
AU - Krzyaniak, Matthew D.
AU - Fitzpatrick, Paul F.
N1 - Publisher Copyright:
© 2015 American Chemical Society.
PY - 2015/6/23
Y1 - 2015/6/23
N2 - Tyrosine hydroxylase is a mononuclear non-heme iron monooxygenase found in the central nervous system that catalyzes the hydroxylation of tyrosine to yield l-3,4-dihydroxyphenylalanine, the rate-limiting step in the biosynthesis of catecholamine neurotransmitters. Catalysis requires the binding of tyrosine, a tetrahydropterin, and O2 at an active site that consists of a ferrous ion coordinated facially by the side chains of two histidines and a glutamate. We used nitric oxide as a surrogate for O2 to poise the active site iron in an S = 3/2 {FeNO}7 form that is amenable to electron paramagnetic resonance (EPR) spectroscopy. The pulsed EPR method of hyperfine sublevel correlation (HYSCORE) spectroscopy was then used to probe the ligands at the remaining labile coordination sites on iron. For the complex formed by the addition of tyrosine and nitric oxide, TyrH/NO/Tyr, orientation-selective HYSCORE studies provided evidence of the coordination of one H2O molecule characterized by proton isotropic hyperfine couplings (Aiso = 0.0 ± 0.3 MHz) and dipolar couplings (T = 4.4 and 4.5 ± 0.2 MHz). These data show complex HYSCORE cross peak contours that required the addition of a third coupled proton, characterized by an Aiso of 2.0 MHz and a T of 3.8 MHz, to the analysis. This proton hyperfine coupling differed from those measured previously for H2O bound to {FeNO}7 model complexes and was assigned to a hydroxide ligand. For the complex formed by the addition of tyrosine, 6-methyltetrahydropterin, and NO, TyrH/NO/Tyr/6-MPH4, the HYSCORE cross peaks attributed to H2O and OH- for the TyrH/NO/Tyr complex were replaced by a cross peak due to a single proton characterized by an Aiso of 0.0 MHz and a dipolar coupling (T = 3.8 MHz). This interaction was assigned to the N5 proton of the reduced pterin.
AB - Tyrosine hydroxylase is a mononuclear non-heme iron monooxygenase found in the central nervous system that catalyzes the hydroxylation of tyrosine to yield l-3,4-dihydroxyphenylalanine, the rate-limiting step in the biosynthesis of catecholamine neurotransmitters. Catalysis requires the binding of tyrosine, a tetrahydropterin, and O2 at an active site that consists of a ferrous ion coordinated facially by the side chains of two histidines and a glutamate. We used nitric oxide as a surrogate for O2 to poise the active site iron in an S = 3/2 {FeNO}7 form that is amenable to electron paramagnetic resonance (EPR) spectroscopy. The pulsed EPR method of hyperfine sublevel correlation (HYSCORE) spectroscopy was then used to probe the ligands at the remaining labile coordination sites on iron. For the complex formed by the addition of tyrosine and nitric oxide, TyrH/NO/Tyr, orientation-selective HYSCORE studies provided evidence of the coordination of one H2O molecule characterized by proton isotropic hyperfine couplings (Aiso = 0.0 ± 0.3 MHz) and dipolar couplings (T = 4.4 and 4.5 ± 0.2 MHz). These data show complex HYSCORE cross peak contours that required the addition of a third coupled proton, characterized by an Aiso of 2.0 MHz and a T of 3.8 MHz, to the analysis. This proton hyperfine coupling differed from those measured previously for H2O bound to {FeNO}7 model complexes and was assigned to a hydroxide ligand. For the complex formed by the addition of tyrosine, 6-methyltetrahydropterin, and NO, TyrH/NO/Tyr/6-MPH4, the HYSCORE cross peaks attributed to H2O and OH- for the TyrH/NO/Tyr complex were replaced by a cross peak due to a single proton characterized by an Aiso of 0.0 MHz and a dipolar coupling (T = 3.8 MHz). This interaction was assigned to the N5 proton of the reduced pterin.
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U2 - 10.1021/acs.biochem.5b00363
DO - 10.1021/acs.biochem.5b00363
M3 - Article
C2 - 26024204
AN - SCOPUS:84934919859
VL - 54
SP - 3759
EP - 3771
JO - Biochemistry
JF - Biochemistry
SN - 0006-2960
IS - 24
ER -