TALENT: Engineering human tyrosine ammonia lyase (TAL) enzymes to treat inborn errors of tyrosine metabolism

Inborn errors of tyrosine metabolism (TIMD) comprise five rare monogenetic disorders of the tyrosine degradation pathway with unmet therapeutic needs. TIMD stop patients' bodies from completely breaking down the amino acid tyrosine. This results in the production and accumulation of toxic metabolites that cause severe illness or even death of the patients. Currently, drug therapy with NTBC is the only effective treatment for many TIMDs. However, it leads to
tyrosine accumulation in the body and is associated with debilitating side-effects.
Here, we want to explore aromatic amino acid ammonia lyases as a new therapeutic approach to restore tyrosine degradation in TIMD patients. These enzymes, which are structurally conserved, catalyze the deamination of histidine (HAL), phenylalanine (PAL), and tyrosine (TAL) into harmless aryl acids and ammonia. The substrate specificity is defined by a selectivity region within the active site. In humans, only HAL enzymes (HuHAL) exist and are expressed in
hepatocytes.
In the TALENT project, we will first re-engineer HuHAL into enzymes with TAL activity by switching its substrate specificity using a directed protein evolution (DPE) approach. Next, we will increase their metabolic activity through iterative rounds of DPE, resulting in hyperactive HuTAL enzymes. Finally, we will integrate HuTAL in viral vectors with liver tropism and study its therapeutic effect in mice and iPSC-derived hepatocytes mimicking different TIMD.