The molecular mechanism of substrate recognition and catalysis of the membrane acyltransferase patA from mycobacteria

Session: 
S7.2 Bacterial cell-wall modification
Code: 
OL7.2.1
Location (hall): 
Mannose
Start/end time: 
Wednesday, July 3, 2019 - 11:45 to 12:00
Itxaso
Anso

Itxaso Anso1, Beatriz  Trastoy1, Montse Tersa1, Alberto Marina1, David Albesa-Jove1, Marcelo Guerin1

1Structural Biology Lab, CIC bioGUNE, Derio, Spain

The biosynthesis of phospholipids and glycolipids are critical pathways for virtually all cell membranes. PatA is an essential membrane associated acyltransferase involved in the biosynthesis of mycobacterial phosphatidyl-myo-inositol mannosides (PIMs). The enzyme transfers a palmitoyl moiety from palmitoyl–CoA to the 6-position of the mannose ring linked to 2-position of inositol in PIM1/PIM2. 

We report here the crystal structures of PatA from Mycobacterium smegmatis in the presence of a nonhydrolyzable palmitoyl–CoA analog and 6-O-palmitoyl-α-D-mannopyranoside, unraveling the acyl donor and acceptor binding mechanism. 

The structures reveal an a/b architecture, with the acyl chain deeply buried into a hydrophobic pocket that runs perpendicular to a long groove where the active site is located. Enzyme catalysis is mediated by an unprecedented charge relay system, which markedly diverges from the canonical HX4D motif.

 By the use of combined structural and quantum-mechanics/molecular-mechanics (QM/MM) metadynamics, we unravel the catalytic mechanism of PatA at the atomic-electronic level. Our studies provide a detailed structural rationale for a stepwise reaction, with the generation of a tetrahedral transition state for the rate-determining step. 

Altogether, our work establishes the mechanistic basis of substrate/membrane recognition and catalysis for an important family of acyltransferases, providing exciting possibilities for inhibitor design.

Overall structure of PatA. a. Cartoon representation showing the general fold and secondary structure organization of PatA. Secondary structure elements are labelled. The central core b-sheet is shown in orange. b. Surface representation of PatA showing the location of the main groove and the active site. The groove entrance is flanked by two important a-helices, a11– a12. The groove ends up into a cavity mainly flanked by a4. c. The main groove runs perpendicular to a hydrophobic tunnel, which is deeply buried into the core of PatA.

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