Detailed analysis of the Catalytic mechanism of Human Glutamine Synthetase

FEDERICO M. ISSOGLIO; ARI ZEIDA; NICOLAS CAMPOLO; RAFAEL RADI; SILVINA BARTESAGHI; DARIO ESTRIN

Mar del Plata

Congreso; 19. LI Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2015

Glutamine synthetase (GS) catalyzes the formation of glutamine from glutamate and ammonia, using ATP as a cofactor. In plants and bacteria it is essential in nitrogen metabolism, making it a good target for herbicides and antimicrobial drug design. In human's brain it prevents glutamate dependent excitotoxicity and detoxifies ammonia. The loss of GS activity as been related with neurodegenerative disorders, such as Alzheimer's disease. The human enzyme has 373 aminoacids (M.W. 44 kDa.) and exists as a decamer, formed by two stacked pentamers, with the active sites located at the interface between two subunits of the pentamer. Mainly from crystallographic results a reaction mechanism has been proposed, but since there is no information regarding the enzyme structure with its three natural substrates, a detailed study of the catalytic mechanism has still not been reported.In the present work we used molecular dynamics simulations (MD), and combined quantum mechanics and molecular mechanics simulations (QM/MM), to examine human GS structural properties, as well as the reaction mechanism at an atomic level. The results provided an accurate study of human GS dynamics, and establishes the groundwork for the analysis of changes in GS activity due to post-translational modifications, as the inactivation of GS through nitration of tyrosine residues by action of peroxynitrite.