Thiolases are a ubiquitous group of enzymes that are involved in biosynthetic and degradative pathways of lipid metabolism. It is therefore necessary to biochemically and structurally characterize these enzymes. The abundance and importance of lipid metabolizing enzymes in Mycobacteria make them attractive targets for drug discovery. Apart from providing energy, lipids and fatty acids also form an integral part of the cell wall and cell membrane of Mycobacteria. The mycobacterial genome codes for over a hundred enzymes involved in fatty acid degradation. A striking feature in all these genomes is the abundance of genes coding for enzymes involved in fatty acid and lipid metabolism more than 250 in Mycobacterium tuberculosis compared to only 50 in Escherichia coli. To date, twenty eight genomes of mycobacterial species have been sequenced completely. The genus Mycobacterium comprises some of the most devastating pathogens that infect both animals and humans. These studies show that MsTLP1 belongs to a new group of thiolase related proteins of unknown function. This is the first structural report of a monomeric thiolase-like protein from any organism. Consistent with this observation, activity measurements show that MsTLP1 does not catalyze the thiolase reaction. Detailed sequence and structural comparisons with thiolases show that the residues known to be essential for catalysis are not conserved in MsTLP1. Interestingly, it consists of six β-strands forming an anti-parallel β-barrel which is completely different from the expected SCP2-fold. An extra C-terminal domain is indeed observed. The structure of the protomer confirms that the N-terminal domain has the thiolase fold. Its structure has been determined at 2.7 Å resolution by the single wavelength anomalous dispersion method. Unlike classical thiolases, MsTLP1 is a monomer in solution. smegmatis protein selected in the present study, referred to here as the thiolase-like protein type 1 ( MsTLP1), has been biochemically and structurally characterized. The mammalian SCP2-thiolase consists of an N-terminal thiolase domain followed by an additional C-terminal domain called sterol carrier protein-2 or SCP2. smegmatis genes have been annotated as thiolases of the poorly characterized SCP2-thiolase subfamily. Thiolases catalyze the Claisen condensation of two acetyl-Coenzyme A molecules in the synthetic direction and the thiolytic cleavage of 3-ketoacyl-Coenzyme A molecules in the degradative direction. They occur as either dimers or tetramers. Thiolases are an important family of enzymes that are involved in fatty acid metabolism.
An analysis of the Mycobacterium smegmatis genome suggests that it codes for several thiolases and thiolase-like proteins.
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