A novel pathway for protein lipoylation in Bacillus subtilis

MARTIN, N; QUIN CHRISTENSEN; JOHN CRONAN; DE MENDOZA; MANSILLA, MC

Puerto Madryn

Congreso; XLVI Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

SAIB

Lipoic acid (LA), a covalently bound cofactor, is essential for the function of several key enzymes involved in oxidative and single carbon metabolism. The current model for protein lipoylation involves two pathways: one in which exogenous LA is transferred to apoproteins in a process mediated by LA ligase A (LplA), and an endogenous one, that involves LipB, which transfers octanoic acid to target proteins. These octanoylated domains are converted into lipoylated derivatives by lipoyl synthase (LipA). We have previously shown that B. subtilis is able to synthesize LA, and if exogenously provided, ligate it to apoproteins. We have also demonstrated that LipL and LipM are essential for the endogenous lipoylation pathway. However, the role of each of these proteins was not clear.In this work we performed physiological and biochemical characterization of different LA auxotrophic mutants and used in vitro biochemical assays that allowed us to conclude that B. subtilis protein lipoylation is carried out through a novel mechanism. This pathway involves the sequential action of LipM and LipL and a third protein, the glycine cleavage system H protein, which acts as a previously undescribed lipoyl/octanoyl carrier. Notably, in B. subtilis four proteins, LipM, GcvH, LipL, and LipA, are essential for the endogenous protein lipoylation pathway, instead of the two-protein model of E. coli.