Structural basis of inhibition of lipid-linked oligosaccharide flippase PglK by a conformational nanobody
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Date
2017-04-19
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Journal Article
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yes
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Abstract
PglK is an ABC transporter that flips a lipid-linked oligosaccharide (LLO) that serves as a donor in protein N-glycosylation. Previous structures revealed two inward-facing conformations, both with very large separations of the nucleotide binding domains (NBDs), and a closed, ADP-bound state that featured an occluded cavity. To investigate additional states, we developed conformation-sensitive, single-domain camelid nanobodies (Nb) and studied their effect on PglK activity. Biochemical, structural, and mass spectrometric analyses revealed that one inhibitory Nb binds as a single copy to homodimeric PglK. The co-crystal structure of this Nb and ADP-bound PglK revealed a new, narrowly inward-open conformation. Rather than inducing asymmetry in the PglK homodimer, the binding of one Nb results in steric constraints that prevent a second Nb to access the symmetry-related site in PglK. The Nb performed its inhibitory role by a “sticky-doorstop” mechanism, where inhibition of ATP hydrolysis and LLO flipping activity occurs due to impaired closing of the NBD interface, which prevents PglK from converting to an outward-open conformation. This inhibitory mode suggests tight conformational coupling between the ATPase sites, which may apply to other ABC transporters.
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published
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Journal / series
Volume
7
Pages / Article No.
46641
Publisher
Nature
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Subject
X-Ray Crystallography; Biochemistry
Organisational unit
03430 - Zenobi, Renato / Zenobi, Renato
03652 - Locher, Kaspar / Locher, Kaspar
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Funding
166672 - Structural and mechanistic studies of components of bacterial protein N-glycosylation pathway and of vitamin B12 transport (SNF)