Stabilization of tryptophan hydroxylase 2 by l-phenylalanine-induced dimerization

Area of Science:

• Biochemistry
• Molecular Biology
• Neuroscience

Background:

• Tryptophan hydroxylase 2 (TPH2) is crucial for serotonin biosynthesis, a neurotransmitter implicated in various psychiatric disorders.
• Full-length TPH2 is challenging to study due to low yields from inherent instability.
• Truncated variants of human TPH2 (rcTPH2, NΔ47-rcTPH2, cTPH2) were created to investigate stability and characterization.

Purpose of the Study:

• To characterize truncated variants of human TPH2 (hTPH2) and assess the impact of ligands on their stability and oligomeric state.
• To identify strategies for improving purification yields and facilitating the structural and functional analysis of hTPH2.

Main Methods:

• Expression and purification of three truncated variants of hTPH2.
• Analysis of thermal stability using differential scanning calorimetry and differential scanning fluorimetry.
• Investigation of oligomeric state using analytical gel filtration.
• Assessment of ligand effects (l-Trp, l-Phe) on stability and oligomerization.

Main Results:

• The catalytic domain variant (cTPH2) showed significantly higher stability compared to variants containing the regulatory domain (rcTPH2, NΔ47-rcTPH2).
• Ligand binding (l-Trp, l-Phe) shifted unfolding transitions and induced a shift towards dimerization for rcTPH2 and NΔ47-rcTPH2.
• l-Phenylalanine (l-Phe) significantly increased the half-lives and stabilized the protein variants.
• Addition of l-Phe to the purification buffer substantially improved purification yields.

Conclusions:

• The regulatory domain of TPH2 contributes to its instability.
• Ligand-induced dimerization, particularly by l-Phe, enhances the stability of TPH2 variants.
• Optimized purification strategies using l-Phe can overcome previous limitations, enabling detailed characterization of hTPH2.