Integral membrane proteins (IMPs) are the biological gateways into and out of cells from all domains of life. IMPs represent between 15 and 30% of the proteomes of most organisms and are the targets for 40 to 50% of currently available FDA-approved drugs, including those that treat allergies, stomach ulcers, gastro-esophageal reflux disease, and schizophrenia, emphasizing their critical importance to the pharmaceutical industry. In addition, a number of membrane-associated proteins have been implicated in the pathogenesis of neurological disorders and viral entry via membrane fusion. Ultimately, robust measurements of IMP structure, dynamics, and function are needed to improve drug discovery and therapeutic development, and enable the elucidation of disease mechanisms.
IMPs are challenging targets for structural and biophysical studies. Of the over 100,000 protein structures deposited in the Protein Data Bank, only approximately 3% are for IMPs. One reason for this paucity of structures is that IMPs must be studied under conditions that closely mimic the cellular environment, namely, the bilayer lipid membrane. Many studies to date have relied on detergents to solubilize and stabilize IMPs, but such preparations do not effectively substitute for the native membrane environment. Furthermore, not all available measurement tools are compatible with these reconstituted IMP systems.
To address this challenge, NIST and IBBR scientists are working to establish robust approaches for functional IMP reconstitution in ‘native-like’ model bilayer lipid membranes, and to develop novel measurement techniques based upon cold neutron scattering, surface plasmon resonance (SPR), electrochemical impedance spectroscopy (EIS), and ultra-high-field nuclear magnetic resonance (UHF-NMR) spectroscopy. A particular focus of the researchers at IBBR is the synthesis of cell membrane model systems, referred to as tethered bilayer lipid membranes (tBLMs), that can be immobilized on surfaces. Collectively, this highly interdisciplinary effort seeks to bridge the gap from techniques based upon detergent-solubilized IMPs to studying the structure, dynamics, and function of IMPs in biologically-relevant membrane environments. Numerous external collaborations have been forged to advance this work with research institutes in the U.S. and abroad, including Carnegie Mellon University, NSF, NIH, and Vilnius University.