Allosteric modulation of peroxisomal membrane protein recognition by farnesylation of the peroxisomal import receptor PEX19

Abstract

The transport of peroxisomal membrane proteins (PMPs) requires the soluble PEX19 protein as chaperone and import receptor. Recognition of cargo PMPs by the C-terminal domain (CTD) of PEX19 is required for peroxisome biogenesis in vivo. Farnesylation at a C-terminal CaaX motif in PEX19 enhances the PMP interaction, but the underlying molecular mechanisms are unknown. Here, we report the NMR-derived structure of the farnesylated human PEX19 CTD, which reveals that the farnesyl moiety is buried in an internal hydrophobic cavity. This induces substantial conformational changes that allosterically reshape the PEX19 surface to form two hydrophobic pockets for the recognition of conserved aromatic/aliphatic side chains in PMPs. Mutations of PEX19 residues that either mediate farnesyl contacts or are directly involved in PMP recognition abolish cargo binding and cannot complement a ΔPEX19 phenotype in human Zellweger patient fibroblasts. Our results demonstrate an allosteric mechanism for the modulation of protein function by farnesylation.

The peroxisome biogenesis factors Pex3 and Pex19: multitasking proteins with disputed functions

“…It is this ahelix that interacts with PMPs [57]. Farnesylation of the CaaX box leads to conformational changes in PEX19 and strongly increases its binding affinity for multiple PMPs [58], a finding that is also reported for the yeast S. cerevisiae [55]. In turn, cargo-bound PEX19 has a higher PEX3-binding affinity than unbound PEX19 [59].…”

Peroxisome biogenesis, membrane contact sites, and quality control

“…A role for the farnesylation of Pex19 is still unclear. Pex19 does not seem to require farnesylation to associate with membranes, and there are reports that it functions to allosterically modulate Pex19 function . Nuclear magnetic resonance data suggest that the C‐terminal residues of the CTD become rigid upon farnesylation, which in turn, might enhance the interactions of mammalian PEX19 with PMPs .…”

Peroxisome prognostications: Exploring the birth, life, and death of an organelle

“…Pex19 is composed of an unstructured N-terminal domain and a structured and globular C-terminal domain (Emmanouilidis et al, 2017). The N-terminal domain is highly flexible with unfolded disordered domains interspersed by five segments capable of forming amphipathic α helices (Schmidt et al, 2010;Chen et al, 2014).…”

“…Almost all Pex19 proteins have a C-terminal farnesylation CAAX motif. When the motif is farnesylated, a hydrophobic pocket that forms part of the mPTS binding site incorporates the farnesyl moiety (Emmanouilidis et al, 2017). Farnesylation induces structural rearrangements within the C-terminal globular domain of Pex19, increasing its rigidity and enhancing its affinity for the mPTS of PMPs (Rucktäschel et al, 2009).…”

“…Farnesylation induces structural rearrangements within the C-terminal globular domain of Pex19, increasing its rigidity and enhancing its affinity for the mPTS of PMPs (Rucktäschel et al, 2009). These rearrangements have been proposed to function as an allosteric regulator of Pex19 binding of PMPs (Emmanouilidis et al, 2017). However, once Pex19 binds a PMP, it is not known how PMP release from Pex19 is mediated or coordinated with Pex19 function.…”