Structural and functional analyses of mutations of the human phenylalanine hydroxylase gene

BackgroundPhenylketonuria (PKU) is an inborn error of metabolism that results from a deficiency of phenylalanine hydroxylase (PAH). We demonstrated PAH mutational spectrum from patients with PKU, including 10 novel and 3 tetrahydrobiopterin (BH4)-responsive mutations. In this study, 11 PAH missense mutations, including 6 novel mutations (P69S, G103S, L293M, G332V, S391I, A447P) found in our previous study, 2 mutations common in east Asian patients with PKU (R243Q, R413P), and 3 tetrahydrobiopterin (BH4)-responsive mutations (R53H, R241C, R408Q) have been functionally and structurally analyzed.MethodsA transient protein overexpression system and an in vitro BH4-responsiveness study were used. The effects of PAH missense mutations on the PAH protein structure were also analyzed. To determine the conservation of 12 mutated residues, PAH was aligned using BLAST against full genomic sequences of 221 different species. Model structures of PAH protein and the composite tetramer were constructed using the software program, SHEBA.ResultsNo PAH activity was detected for some mutants. However, the residual activities associated with other mutants ranged over a wide spectrum. The missense mutations responsive to BH4 were not highly conserved throughout the 43 species in the multiple sequence alignment that encode PAH. The composite model structure of PAH revealed that dimer stability was reduced in the BH4-responsive mutants, whereas tetramer stability remained normal.ConclusionThis expression study analyzed PAH mutations and model structures of mutant PAH proteins are proposed. Correlation between the proposed mutant PAH structures and functions are suggested.