Divergence in enzyme regulation between Caenorhabditis elegans and human tyrosine hydroxylase, the key enzyme in the synthesis of dopamine

11 páginas, 5 figuras, 2 tablas.TH (tyrosine hydroxylase) is the rate-limiting enzyme in the synthesis of catecholamines. The cat-2 gene of the nematode Caenorhabditis elegans is expressed in mechanosensory dopaminergic neurons and has been proposed to encode a putative TH. In the present paper, we report the cloning of C. elegans full-length cat-2 cDNA and a detailed biochemical characterization of the encoded CAT-2 protein. Similar to other THs, C. elegans CAT-2 is composed of an N-terminal regulatory domain followed by a catalytic domain and a C-terminal oligomerization domain and shows high substrate specificity for L-tyrosine. Like hTH (human TH), CAT-2 is tetrameric and is phosphorylated at Ser35 (equivalent to Ser40 in hTH) by PKA (cAMP-dependent protein kinase). However, CAT-2 is devoid of characteristic regulatory mechanisms present in hTH, such as negative co-operativity for the cofactor, substrate inhibition or feedback inhibition exerted by catecholamines, end-products of the pathway. Thus TH activity in C. elegans displays a weaker regulation in comparison with the human orthologue, resembling a constitutively active enzyme. Overall, our data suggest that the intricate regulation characteristic of mammalian TH might have evolved from more simple models to adjust to the increasing complexity of the higher eukaryotes neuroendocrine systems.This study was supported by The Research Council of Norway, the Meltzer Fond and the Instituto de Salud Carlos III [project numbers PI050065 and PI080557], co-financed with the Fondo Europeo de Desarrollo Regional (FEDER), and Junta de Andalucía [project numbers P07-CVI-02697 and P08-CVI-03629]. A.L.P. is a recipient of a Ramon y Cajal contract from the Spanish Ministry of Science and Innovation (MICINN).Peer reviewe