Structural basis for selective recognition of acyl chains by the membrane-associated acyltransferase PatA

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 its naturally occurring acyl donor palmitate and a nonhydrolyzable palmitoyl-CoA analog. The structures reveal an alpha/beta 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. Our studies establish the mechanistic basis of substrate/membrane recognition and catalysis for an important family of acyltransferases, providing exciting possibilities for inhibitor design.This work was supported by the European Commission Contract HEALTH-F3-2011-260872, the Spanish Ministry of Economy and Competitiveness Contract BIO2013-49022-C2-2-R, and the Basque Government (to M.E.G.); Slovak Research and Development Agency Contract No. DO7RP-0015-11 (to K.M.) and the NIH/NIAID grant AI064798 (to M.J.). D.A.-J. acknowledges the support from Fundacion Biofisica Bizkaia. We gratefully acknowledge Sonia Lopez-Fernandez (Unit of Biophysics, CSIC, UPV/EHU, Spain), Drs E. Ogando and T. Mercero (Scientific Computing Service UPV/EHU, Spain) for technical assistance. We thank the Swiss Light Source (SLS), and the Diamond Light Source (DLS) for granting access to synchrotron radiation facilities and their staff for the onsite assistance. We specially thank the BioStruct-X project to support access to structural biology facilities. We also acknowledge all members of the Structural Glycobiology Group (Spain) for valuable scientific discussions. The following reagent was obtained through BEI Resources, NIAID, NIH: Mycobacterium tuberculosis, Strain H37Rv, Purified Phosphatidylinositol Mannosides 1 and 2 (PIM1,2), NR-14846