NMR structure of AbhN and comparison with AbrBN: FIRST insights into the DNA binding promiscuity and specificity of AbrB-like transition state regulator proteins.

Understanding the molecular mechanisms of transition state regulator proteins is critical, since they play a pivotal role in the ability of bacteria to cope with changing environments. Although much effort has focused on their genetic characterization, little is known about their structural and functional conservation. Here we present the high resolution NMR solution structure of the N-terminal domain of the Bacillus subtilis transition state regulator Abh (AbhN), only the second such structure to date. We then compare AbhN to the N-terminal DNA-binding domain of B. subtilis AbrB (AbrBN). This is the first such comparison between two AbrB-like transition state regulators. AbhN and AbrBN are very similar, suggesting a common structural basis for their DNA binding. However, we also note subtle variances between the AbhN and AbrBN structures, which may play important roles in DNA target specificity. The results of accompanying in vitro DNA-binding studies serve to highlight binding differences between the two proteins.