BH4 responsiveness associated to a PKU mutation with decreased binding affinity for the cofactor.
BACKGROUND
Tetrahydrobiopterin (BH4), cofactor of phenylalanine hydroxylase, can be used to treat a subset of phenylketonuria (PKU) patients as it results in a reduction in blood phenylalanine levels. The molecular basis of the response appears to be multifactorial.


METHODS
A standard BH4 loading test (20 mg/kg) was performed. Genotyping was performed by DGGE and sequencing analysis. Expression analysis of the D129G mutation was performed in E. coli (expression as fusion protein MBP-PAH) and in a human hepatoma cell line with an N-terminal FLAG epitope.


RESULTS
We report the positive response and long-term treatment of a patient functionally hemizygous for the D129G mutation in the phenylalanine hydroxylase gene. Expression in the prokaryotic system revealed partial activity and a decreased binding affinity for BH4 of the mutant protein. In the eukaryotic system the mutant protein shows reduced stability.


CONCLUSIONS
The D129G mutation which confers a BH4-responsive phenotype, has a decreased binding affinity for BH4.
Aguado
Cristina
C
Centro de Biología Molecular Severo Ochoa CSIC-UAM, Madrid, Spin.
Pérez
Belen
B
García
M José
MJ
Bélanger-Quintana
Amaya
A
Martínez-Pardo
Mercedes
M
Ugarte
Magdalena
M
Desviat
Lourdes R
LR
D001708:Biopterins / Q000031:analogs & derivatives* / Q000494:pharmacology; D004252:DNA Mutational Analysis; D005838:Genotype; D006801:Humans; D007231:Infant, Newborn; D009154:Mutation / Q000235:genetics*; D015997:Neonatal Screening; D019001:Nitric Oxide Synthase / Q000378:metabolism; D010641:Phenotype; D010649:Phenylalanine; D010651:Phenylalanine Hydroxylase / Q000235:genetics* / Q000378:metabolism; D010661:Phenylketonurias / Q000175:diagnosis* / Q000235:genetics*; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
D011993:Recombinant Fusion Proteins; D001708:Biopterins; D010649:Phenylalanine; D019001:Nitric Oxide Synthase; D010651:Phenylalanine Hydroxylase; C003402:sapropterin