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1HYO is an EC 3.7.1.2 hydrolase involved in the final step of the Phe/Tyr catabolic pathway, and producing [Fumarate and Acetoacetate].

The mechanism is not well understood, but is hypothesized that His-133 activates a nucleophilic water, which attacks the δ carbon, leading to cleavage^[1]. The resultant tetrahedral alkoxy transition state is thought to be stabilized by Arg-237, Gln-240, and Lys-253 residues. As with all of the EC 3.7.1 class enzymes, the key to the C-C cleavage is the metal ion that lines up with the carbon to be cleaved.

Disease and Treatment

Mutations in 1HYO are responsible for hereditary tyrosemia Type I, a serious metabolic disease resulting in chronic inflammation of the liver and neuronal damage^[2]. It is in the same metabolic pathway as Phenylketonuria (PKU) in infants, and is treated similarly with strict lifelong dietary control and pharmacological inhibition of [Phenylalanine hydroxylase], the key first enzyme in the degradation pathway.

In very serious acute cases, double liver/kidney transplant may be considered as an option as well.

Relevance

Structural highlights

FAH is a homodimer made up of two 46 kDa subunits. The subunits form a cavity ^[3]. The binding is coordinated by Ca2+, Arg and two Tyr. The active residues in are His-133, acting as a base to activate a water, and Arg-237, Gln-240 and Lys-253 acting to stabilize the tetrahedral alkoxy transition state.

References

1. ↑ Bateman, R.L., Bhanumoorthy, P., Witte, J.F., McClard, R.W., Grompe, M., Timm, D.E. (2001) Mechanistic Inferences from the Crystal Structure of Fumarylacetoacetate Hydrolase with a Bound Phosphorus-based Inhibitor. Journal of Biological Chemistry, 207(18) 15284-15291
2. ↑ Grompe, M. (2001)The Pathophysiology and Treatment of Hereditary Tyrosinemia Type 1. Liver Diease, 21(4):563-572 DOI:10.1055/s-2001-19035
3. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named main_paper