Insights into transport mechanism from LeuT engineered to transport tryptophan

Journal Article · Tue Jan 10 04:00:00 EST 2012 · EMBO Journal

DOI:https://doi.org/10.1038/emboj.2011.353· OSTI ID:1033019

Piscitelli, Chayne L; Gouaux, Eric ^[1]

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1. Oregon HSU

LeuT is a bacterial homologue of the neurotransmitter:sodium symporter (NSS) family and, being the only NSS member to have been structurally characterized by X-ray crystallography, is a model protein for studying transporter structure and mechanism. Transport activity in LeuT was hypothesized to require structural transitions between open-to-out and occluded conformations dependent upon protein:ligand binding complementarity. Here, using crystallographic and functional analysis, we show that binding site modification produces changes in both structure and activity that are consistent with complementarity-dependent structural transitions to the occluded state. The mutation I359Q converts the activity of tryptophan from inhibitor to transportable substrate. This mutation changes the local environment of the binding site, inducing the bound tryptophan to adopt a different conformer than in the wild-type complex. Instead of trapping the transporter open, tryptophan binding now allows the formation of an occluded state. Thus, transport activity is correlated to the ability of the ligand to promote the structural transition to the occluded state, a step in the transport cycle that is dependent on protein:ligand complementarity in the central binding site.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: NIH
• OSTI ID: 1033019
• Journal Information: EMBO Journal, Journal Name: EMBO Journal Journal Issue: 1 Vol. 31; ISSN EMJODG; ISSN 0261-4189
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
60 APPLIED LIFE SCIENCES
CRYSTALLOGRAPHY
FUNCTIONAL ANALYSIS
MODIFICATIONS
MUTATIONS
PROTEINS
TRANSPORT
TRAPPING
TRYPTOPHAN