Steric occlusion regulates proximal interactions of acyl carrier protein domain in fungal fatty acid synthase

Jennifer W Lou,Mohammad T Mazhab-Jafari

doi:10.1038/s42003-020-0997-y

Abstract

The acyl carrier protein (ACP) domain shuttles substrates and reaction intermediates in type I fungal fatty acid synthases via transient protein-protein interactions. Here, using electron cryo-microscopy (cryoEM), we report the structure of a fungal FAS stalled at the dehydration reaction, which precedes the final enoyl reduction in the fatty acid biosynthesis cycle. This conformation revealed multiple contact sites between ACP and the dehydratase (DH) and enoyl reductase (ER) domains that occluded the ACP binding to the adjacent ER domain. Our data suggests a minimal path from the DH to the ER reaction site that requires minute changes in the coordinates of the structured N- and C- termini of the ACP domain.

Highlights

The acyl carrier protein (ACP) domain shuttles substrates and reaction intermediates in type I fungal fatty acid synthases via transient protein-protein interactions
Low resolution (~20 Å) densities with weak signal-to-noise ratio (S/N) are observed in proximity of other catalytic centers in a cryoEM map of S. cerevisiae FAS12 that allowed for approximate placement of ACP models in proximity of ketoacyl synthase (KS), ketoacyl reductase (KR), enoyl reductase (ER), and acetyltransferase (AT) domains albeit with ambiguity in ACP orientation
The cryoEM map of the complex shows the global localization of ACP at the KS domain (Fig. 1e and Supplementary Fig. 3) as observed in a previously reported map of endogenous fatty acid synthases (FAS) from S. cerevisiae[14]

Summary

Introduction

The acyl carrier protein (ACP) domain shuttles substrates and reaction intermediates in type I fungal fatty acid synthases via transient protein-protein interactions. Using electron cryo-microscopy (cryoEM), we report the structure of a fungal FAS stalled at the dehydration reaction, which precedes the final enoyl reduction in the fatty acid biosynthesis cycle. This conformation revealed multiple contact sites between ACP and the dehydratase (DH) and enoyl reductase (ER) domains that occluded the ACP binding to the adjacent ER domain. Enzymes responsible for synthesis of the lipid precursor palmitate, a 16-carbon chain hydrocarbon molecule, are collectively known as fatty acid synthases (FAS) and are conserved from bacteria to humans[4]. Recent cryoEM studies have observed sub-nanometer resolution ACP densities proximal to KS13,14, ER14,15, and AT16 domains in the apo state of FAS enzymes purified from different fungal species

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