Monomer-dimer Equilibrium of Mycobacterium tuberculosis Alanine Racemase Depends on Buffer Conditions

Abstract

(Azam and Jayaram, 2016). Several known inhibitors of M. tuberculosis ALR (Mt-ALR) work by binding to the substrate-binding site proximal to the bound PLP (Anthony et al., 2011). Among known inhibitors of Mt-ALR, only D-cycloserine, a substrate analog, is used medically to treat TB. However, D-cycloserine carries substantial side effects because it inactivates ALR by binding to the enzyme-bound PLP and PLP-dependent enzymes are essential for many eukaryotic systems. In humans, PLP is important for proper neural functioning. Disruption of PLP binding has led to reports of dizziness, coma, depression, and other neurological and psychotic disorders in D-cycloserine users (Walsh, 2003). Anthony et al. (2011) have identified new classes of ALR inhibitors by high-throughput screening of 53,000 compounds. Upon analyzing synthetic compound libraries, 472 hits were found, with only 25 strong hits. All of the hits came from the synthetic compound libraries analyzed; their strategy was to select inhibitors that are not substrate analogs. Similarly, to avoid selecting the inhibitors that are substrate analogs, some authors have suggested the inclusion of conserved residues at the entrance to the catalytic pocket of Mt-ALR as additional targets in structure-aided drug design (LeMagueres et al., 2005). Others have suggested designing inhibitors that bind to the dimer interface to block dimerization (Azam and Jayaram, 2016). One of the goals of the current study was to understand the dimerization of ALRs and thus aid in the design of inhibitors, which could serve as drugs, that work by interfering with the dimerization of Mt-ALR. ALR has long been recognized as a potential target for drug design (Silverman, 1988). While some species show monomeric ALR, most ALR exhibit dimeric forms (Ju et al., 2011). Yokoigawa et al. (2003) first reported a dynamic monomer-dimer equilibrium in the case of ALR from 4 Shigella species. Ju et al. (2005) Monomer-dimer Equilibrium of Mycobacterium tuberculosis Alanine Racemase Depends on Buffer Conditions