1 research outputs found
The Monomeric Species of the Regulatory Domain of Tyrosine Hydroxylase Has a Low Conformational Stability
Tyrosine
hydroxylase (TyrH) catalyzes the hydroxylation of tyrosine
to form 3,4-dihydroxyphenylalanine, the first step in the synthesis
of catecholamine neurotransmitters. The protein contains a 159-residue
regulatory domain (RD) at its N-terminus that forms dimers in solution;
the N-terminal region of RDTyrH (residues 1–71) is absent in
the solution structure of the domain. We have characterized the conformational
stability of two species of RDTyrH (one containing the N-terminal
region and another lacking the first 64 residues) to clarify how that
N-terminal region modulates the conformational stability of RD. Under
the conditions used in this study, the RD species lacking the first
64 residues is a monomer at pH 7.0, with a small conformational stability
at 25 °C (4.7 ± 0.8 kcal mol<sup>–1</sup>). On the
other hand, the entire RDTyrH is dimeric at physiological pH, with
an estimated dissociation constant of 1.6 μM, as determined
by zonal gel filtration chromatography; dimer dissociation was spectroscopically
silent to circular dichroism but not to fluoresecence. Both RD species
were disordered below physiological pH, but the acquisition of secondary
native-like structure occurs at pHs lower than those measured for
the attainment of tertiary native- and compactness-like arrangements