Aryl carrier proteins

Sheftel, A., StehUng, O., LiU, R. (2010). Iron-sulfur proteins in health and disease. Trends in Endocrinology and Metabolism, 21, 302—314. Zhou, Z., Lai, J. R., Walsh, C. T. (2007). Directed evolution of aryl carrier proteins in the enterobactin synthetase. Proceedings of the National Academy of Sciences of the United States of America, 104, 11621—11626. 

Pathways II and III, found in various fluorescent pseudomonads, supply mainly md-(R)-3HA monomers from fatty acid P-oxidation and fatty acid biosynthesis intermediates, respiec-tively. The intermediates in these pathways are effectively converted by specialized enzymes to generate (R)-3HA-CoA monomers for polymerization. As shown in Figure 3, (R)-spedfic enoyl-CoA hydratase (PhaJ) and (R)-3-HA-ACP-CoA transferase (PhaG ACP, aryl carrier protein) function as metabolic suppliers of (R)-3HA-CoA from fr[Pg.160]

It is noteworthy that nonribosomal peptide synthetase is similarly posttrans-lationally modified by covalent attachment of the 4 -phosphopantetheine group to the peptidyl carrier protein (PCP) [193-198]. While the ACPS can modify various apo-ACPs [167,173,187-189,191,192],it failed to modify PCPs from a variety of peptide synthetases [189]. This led to the discovery of the second family of PPTases [189], such as EntD from E. coli [189, 199, 200], Sfp from Bacillus subtilis [189,200-204], PptT from M. tuberculosis [264], and Gsp from B. brevis [ 189,205,206], required for the biosynthesis of enterobactin, surfactin, mycobactin, and gramicidin S, respectively. In contrast to ACPS, proteins in the latter family, such as Sfp, showed broader substrate specificity, modifying apo-PCPs, apo-ACPs, as well as apo-aryl carrier proteins and utilizing both CoA, acyl CoAs, and CoA analogs [204]. 

The approach using cyclodextrin as a binding site has also been developed. Cyclodextrins are widely utilized in biomimetic chemistry as simple models for an enzyme because they have the ability to form inclusion complexes with a variety of molecules and because they have catalytic activity toward some reactions. Kojima et al. (1980, 1981) reported the acceleration in the reduction of ninhydrin and some dyes by a 1,4-dihydronicotinamide attached to 3 Cyclodextrin. Saturation kinetics similar to enzymatic reactions were observed here, which indicates that the reduction proceeds through a complex. Since the cavity of the cyclodextrin molecule has a chiral environment due to the asymmetry of D-glucose units, these chiralities are expected to be effective for the induction of asymmetry into the substrate. Asymmetric reduction with NAD(P)H models of this type, however, has not been reported. Asymmetric reduction by a 1,4-dihydronicotinamide derivative took place in an aqueous solution of cyclodextrin (Baba et al. 1978), although the optical yield from the reduction was quite low. Trifluoromethyl aryl ketones were reduced by PNAH in 1.1 to 5.8 % e.e. in the presence of 3-cyclodextrin. Sodium borohydride works as well (Table 18). In addition to cyclodextrin, Baba et al. also found that the asymmetric reductions can be accomplished in the presence of bovine serum albumin (BSA) which is a carrier protein in plasma. 

Arylation or alkylation are used for activation of support and linking of a protein ligand. In such reactions, the functional group on the carrier combines with an NH2 group of the protein (e.g., by 3-fluoro-4,6-dinitrophenyl group or 2-4 dichloro-5-triazine). In this approach, a chloro-5-triazine is coupled to an arylazide. The azide is converted to a nitrene, which upon activation by light reacts with a polymer carrier to form a covalent bond. The chlorotriazine then couples with the protein. 

Carbodiimides substances with free aryl or alkyl groups. They are mostly used for the binding of protein to red blood cells, for serologic studies. However these reagents can also be applied to the coupling of some drugs to various carriers... 

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