Biochemical and structural characterization of an essential acyl-CoA carboxylase from Mycobacterium tuberculosis

GAGO, G; KURTH, D; DIACOVICH, L; TSAI, S C; GRAMAJO, HUGO CÉSAR

Journal of Bacteriology

Año: 2006 vol. 188 p. 477 - 486

0021-9193

Pathogenic mycobacteria contain a variety of unique fatty acids that have methyl branches at even-numbered position at the carboxyl end, and a long n-aliphatic chain. One such group of acids, called mycocerosic acids, is found uniquely in the cell wall of pathogenic mycobacteria and their biosynthesis is essential for their growth and pathogenesis. Therefore, the biosynthetic pathway of the unique precursor of such lipids, methylmalonyl-CoA, represents an attractive target for developing new antituberculous drugs. Heterologous protein expression and purification of the individual subunits allowed the successful reconstitution of an essential acyl-CoA carboxylase from Mycobacterium tuberculosis, whose main role appears to be the synthesis of methylmalonyl-CoA. The enzyme complex was reconstituted from the a biotinylated subunit AccA3, the carboxyltransferase b subunit AccD5 and the e subunit AccE5 (Rv3281). The kinetic properties of this enzyme showed a clear substrate preference for propionyl-CoA compared with acetyl-CoA (specificity constant five fold higher), indicating that the main physiological role of this enzyme complex is to generate methylmalonyl-CoA for the biosynthesis of branched-chain fatty acids. The a and b subunits are capable of forming a stable a6/b6 sub-complex but with very low specific activity. The addition of the e subunit, which binds tightly to the a-b sub-complex, is essential for gaining maximal enzyme activity.