Mycobacterium tuberculosis FasR senses long fatty acyl-CoA through a tunnel and a hydrophobic transmission spine

Julia Lara,Nicole Larrieux,Marisa M Fernández,Emilio L Malchiodi,Gabriela Gago,Lautaro Diacovich,Felipe Trajtenberg,Alejandro Buschiazzo,Hugo Gramajo

doi:10.1038/s41467-020-17504-x

Abstract

Mycobacterium tuberculosis is a pathogen with a unique cell envelope including very long fatty acids, implicated in bacterial resistance and host immune modulation. FasR is a TetR-like transcriptional activator that plays a central role in sensing mycobacterial long-chain fatty acids and regulating lipid biosynthesis. Here we disclose crystal structures of M. tuberculosis FasR in complex with acyl effector ligands and with DNA, uncovering its molecular sensory and switching mechanisms. A long tunnel traverses the entire effector-binding domain, enabling long fatty acyl effectors to bind. Only when the tunnel is entirely occupied, the protein dimer adopts a rigid configuration with its DNA-binding domains in an open state, leading to DNA dissociation. The protein-folding hydrophobic core connects the two domains, and is completed into a continuous spine when the effector binds. Such a transmission spine is conserved in a large number of TetR-like regulators, offering insight into effector-triggered allosteric functional control.

Highlights

Mycobacterium tuberculosis is a pathogen with a unique cell envelope including very long fatty acids, implicated in bacterial resistance and host immune modulation
FasR:DNA binding is regulated by long-chain acyl-CoAs, which are themselves products of FAS I, namely acyl-CoAs ≥ C16 disrupt the interaction of Mycobacterium tuberculosis (Mtb) FasR with its cognate DNA6
FasRΔ33 readily crystallised in the absence of added ligands and in complex with acyl C20-CoA. Both crystal forms diffracted X-rays at better than 1.7 Å resolution (Supplementary Table 1), and their structures confirm the dimeric architecture of FasRΔ33, with each protomer organized in two all-helical domains (Fig. 1a), similar to known TFRs10

Summary

Introduction

Mycobacterium tuberculosis is a pathogen with a unique cell envelope including very long fatty acids, implicated in bacterial resistance and host immune modulation. FasR is a TetR-like transcriptional activator that plays a central role in sensing mycobacterial long-chain fatty acids and regulating lipid biosynthesis. The protein-folding hydrophobic core connects the two domains, and is completed into a continuous spine when the effector binds Such a transmission spine is conserved in a large number of TetR-like regulators, offering insight into effector-triggered allosteric functional control. ACP) leading to very long-chain meromycolyl-ACPs (up to C56) The latter are eventually condensed to FAS I-synthetised C24-26 fatty acids to produce mycolic acids. FAS I-derived long-chain acyl-CoAs are used as mycolic acid precursors, and for the biosynthesis of phospholipids, triacylglycerides, polyketides and other complex lipids, relevant for Mtb pathogenicity[4,5]. FasR is essential for Mycobacterium smegmatis viability[6], further highlighting its key role in mycobacterial biology

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