Community Research and Development Information Service - CORDIS



Project ID: 623757
Funded under: FP7-PEOPLE
Country: United Kingdom
Domain: Health, Fundamental Research

Molecular architecture dynamics and membrane transport

Secondary membrane transporter action has wide implications, including drug and nutrient accessibility for target cells. EU researchers have investigated the role molecular architecture plays in interaction with the molecules for delivery.
Molecular architecture dynamics and membrane transport
Secondary active transporters use the existing sodium gradient present inside and outside the cell membrane. Despite their importance in all biological processes, little is known about their molecular structure and how it changes during their transport activities.

Using mass spectrometry (MS) and computer modelling, the TRANSPORTER FUNCTION (Mass spectrometry of structural dynamics in secondary membrane transporters) project has successfully compared two structural models in action during a biological process.

Researchers selected sodium/proton exchangers (periplasmic nitrate reductase (NapA) and Na+/H+ antiporter (NhaA) for study. NapA requires large conformational changes during the transport cycle whereas NhaA is believed to undergo only small structural modifications.

A new MS technique was developed to analyse and compare interactions of NapA and NhaA with membrane lipids. Results show NapA forms stable dimers and retains virtually no lipids after purification, while NhaA dimers dissociate very easily and retain selectively-bound cardiolipin.

Structurally, sequence analysis and homology modelling showed that NapA has an alpha, 13-helix architecture with an additional helix that mediates extensive subunit contacts. NhaA, on the other hand, forms a 12-helix bundle with a very weak dimer interface that lacks the additional helix.

The TRANSPORTER FUNCTION team developed a novel calibration protocol to accurately measure collision cross-sections (CCSs) of low-charge membrane proteins. CCS is a fast-growing field that is revolutionising the quest to determine the multi-component complexes that proteins adopt to perform their functions.

Using this protocol, NapA was found to preferentially interact with charged particles giving rise to ‘molecular grease’ for structural changes in the transport cycle. MS and Molecular dynamics simulations of bilayer membranes showed that NhaA instead uses lipids for dimer stabilization. Based on the different selectivities for functional lipids displayed by the secondary active transporters, TRANSPORTER FUNCTION formulated a sliding scale model for lipid selection in membrane proteins.

Selective binding of membrane lipids enables secondary transporter molecules to change the stability of their molecular complexes. Being able to determine the extent and nature of lipid selection by transporters has immense pharmacological significance. One prime example is its application to a sodium/proton exchanger, a drug target in the treatment of hypertension.

Related information


Molecular architecture, secondary membrane transporter, TRANSPORTER FUNCTION, NapA, NhaA, lipid
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