2 domain LipA function was restored by transduction with cells with phage particles containing a lipA cosmid that had been packaged in vivo. Using this approach two types of labeling AICA Riboside web experiments were done. In the first protocol E2 domains were labeled in vivo by growth in the presence of octanoic d15 acid. Following removal of the labeled octanoate the cells were then resuspended in growth medium and transduced with the packaged lipA-encoding cosmid. Following incubation to allow lipoate synthesis samples were taken and the E2 domain species were isolated, purified, and analyzed by electrospray mass spectroscopy (Fig. 11). In the cultures to which LipA activity was restored a readily detectable conversion of the E2 domain modified with octanoate d15 to a species of 60 additional mass units was seen. This was exactly the increase in mass (gain of two sulfur atoms of mass 32 and loss of two deuterium atoms of mass two) expected for conversion of the d15 labeled octanoyl-E2 domain to the d13-labeled lipoyl-domain. In the second protocol (a variation of the first protocol) the octanoic d15 acid was removed by washing the cells and replaced with normal (non-deuterated) octanoate. This experiment gave essentially the same result; the d15 labeled octanoyl-E2 domain was converted to d13 labeled lipoyl-E2 domain (Fig. 11). A modification of these experiments also showed that octanoyl-PDH accumulated in vivo in a lipA strain was converted to its active form upon restoration of LipA activity (201). The conversion of octanoyl-domain to lipoyl domain was also observed in vitro (201), although the extant of conversion was much less than stoichiometric with LipA. These result were recently confirmed using octanoyl-H protein as the substrate with an eight-fold increase in the yield of lipoic acid formed/LipA monomer (202). As mentioned above lipoic acid synthase is a member of the radical-SAM enzyme superfamily which utilize a reduced iron-sulfur cluster and SAM to generate 5’deoxyadenosyl 5-radicals (5-dA) for further H 4065 chemical information radical-based chemistry (59, 243?46). In the lipoic acid synthase reaction (Fig. 12), it is generally believed that the role of the 5-dA is to remove one hydrogen atom from each of the C-6 and C-8 positions of octanoic acid thereby allowing for subsequent sulfur insertion (202, 240). Consistent with this prediction two molecules of SAM are required to synthesize one mole of lipoyl cofactor (202). This stoichiometry is similar to that obtained in the two studies in the BioB reaction (247, 248) and suggests that the abortive cleavage of SAM observed in these systems might result from some innate reactivity associated with this subclass of radical SAM enzymes (202).Author Manuscript Author Manuscript Author Manuscript Author ManuscriptEcoSal Plus. Author manuscript; available in PMC 2015 January 06.CronanPageAs in the case of biotin the source of the sulfur atoms of lipoic acid is thought to be a [Fe-S] cluster distinct from the SAM radical [4Fe-4S] cluster. In the first successful in vitro lipoic acid synthesis assays, lipoic acid was formed in the absence of exogenous sulfur-containing compounds in the in vitro assay (202, 240). This suggested that, like biotin synthase, the protein itself has some mobilizable sulfur atoms, either from an Fe-S cluster, a persulfide or some other species. The currently favored sulfur source is an iron-sulfur cluster (240, 249). Recent work from the Booker group reported that lipoic acid synthase contains.2 domain LipA function was restored by transduction with cells with phage particles containing a lipA cosmid that had been packaged in vivo. Using this approach two types of labeling experiments were done. In the first protocol E2 domains were labeled in vivo by growth in the presence of octanoic d15 acid. Following removal of the labeled octanoate the cells were then resuspended in growth medium and transduced with the packaged lipA-encoding cosmid. Following incubation to allow lipoate synthesis samples were taken and the E2 domain species were isolated, purified, and analyzed by electrospray mass spectroscopy (Fig. 11). In the cultures to which LipA activity was restored a readily detectable conversion of the E2 domain modified with octanoate d15 to a species of 60 additional mass units was seen. This was exactly the increase in mass (gain of two sulfur atoms of mass 32 and loss of two deuterium atoms of mass two) expected for conversion of the d15 labeled octanoyl-E2 domain to the d13-labeled lipoyl-domain. In the second protocol (a variation of the first protocol) the octanoic d15 acid was removed by washing the cells and replaced with normal (non-deuterated) octanoate. This experiment gave essentially the same result; the d15 labeled octanoyl-E2 domain was converted to d13 labeled lipoyl-E2 domain (Fig. 11). A modification of these experiments also showed that octanoyl-PDH accumulated in vivo in a lipA strain was converted to its active form upon restoration of LipA activity (201). The conversion of octanoyl-domain to lipoyl domain was also observed in vitro (201), although the extant of conversion was much less than stoichiometric with LipA. These result were recently confirmed using octanoyl-H protein as the substrate with an eight-fold increase in the yield of lipoic acid formed/LipA monomer (202). As mentioned above lipoic acid synthase is a member of the radical-SAM enzyme superfamily which utilize a reduced iron-sulfur cluster and SAM to generate 5’deoxyadenosyl 5-radicals (5-dA) for further radical-based chemistry (59, 243?46). In the lipoic acid synthase reaction (Fig. 12), it is generally believed that the role of the 5-dA is to remove one hydrogen atom from each of the C-6 and C-8 positions of octanoic acid thereby allowing for subsequent sulfur insertion (202, 240). Consistent with this prediction two molecules of SAM are required to synthesize one mole of lipoyl cofactor (202). This stoichiometry is similar to that obtained in the two studies in the BioB reaction (247, 248) and suggests that the abortive cleavage of SAM observed in these systems might result from some innate reactivity associated with this subclass of radical SAM enzymes (202).Author Manuscript Author Manuscript Author Manuscript Author ManuscriptEcoSal Plus. Author manuscript; available in PMC 2015 January 06.CronanPageAs in the case of biotin the source of the sulfur atoms of lipoic acid is thought to be a [Fe-S] cluster distinct from the SAM radical [4Fe-4S] cluster. In the first successful in vitro lipoic acid synthesis assays, lipoic acid was formed in the absence of exogenous sulfur-containing compounds in the in vitro assay (202, 240). This suggested that, like biotin synthase, the protein itself has some mobilizable sulfur atoms, either from an Fe-S cluster, a persulfide or some other species. The currently favored sulfur source is an iron-sulfur cluster (240, 249). Recent work from the Booker group reported that lipoic acid synthase contains.
