Structure and Mechanism of Hedgehog Acyl Transferase

Coupland, C. E.; Andrei, S. A.; Ansell, T. B.; Carrique, L.; Kumar, P.; Sefer, L.; Schwab, R. A.; Byrne, E. F. X.; Pardon, E.; Steyaert, J.; Magee, A. I.; Sansom, M. S. P.; Tate, E. W.; Siebold, C.

doi:10.1101/2021.07.08.451580

bioRxiv · 10.1101/2021.07.08.451580

Structure and Mechanism of Hedgehog Acyl Transferase

Coupland, C. E.·Andrei, S. A.·Ansell, T. B.·Carrique, L.·Kumar, P.·Sefer, L.·Schwab, R. A.·Byrne, E. F. X.·Pardon, E.·Steyaert, J.·Magee, A. I.·Sansom, M. S. P.·Tate, E. W.·Siebold, C.

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Abstract

The iconic Sonic Hedgehog (SHH) morphogen pathway is a fundamental orchestrator of embryonic development and stem cell maintenance, and is implicated in cancers in various organs. A key step in signalling is transfer of a palmitate group to the N-terminal cysteine residue of SHH, catalysed by the multi-pass transmembrane enzyme Hedgehog acyltransferase (HHAT) resident in the endoplasmic reticulum (ER). Here, we present the high-resolution cryo-EM structure of HHAT bound to substrate analogue palmityl-coenzyme A and a SHH mimetic megabody. Surprisingly, we identified a heme group bound to an HHAT cysteine residue and show that this modification is essential for HHAT structure and function. A structure of HHAT bound to potent small molecule inhibitor IMP-1575 revealed conformational changes in the active site which occlude substrate binding. Our multidisciplinary analysis provides a detailed view of the novel mechanism by which HHAT adapts the membrane environment to transfer a long chain fatty acid across the ER membrane from cytosolic acyl-CoA to a luminal protein substrate. This structure of a member of the protein-substrate membrane-bound O-acyltransferase (MBOAT) superfamily provides a blueprint for other protein substrate MBOATs, such as WNT morphogen acyltransferase Porcupine and ghrelin O-acyltransferase GOAT, and a template for future drug discovery.

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Coupland, C. E., Andrei, S. A., Ansell, T. B., Carrique, L., Kumar, P., Sefer, L., Schwab, R. A., Byrne, E. F. X., Pardon, E., Steyaert, J., Magee, A. I., Sansom, M. S. P., Tate, E. W., Siebold, C.. 2021-07-09. Structure and Mechanism of Hedgehog Acyl Transferase. https://doi.org/10.1101/2021.07.08.451580

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