ICE | The Israel Chemist and Engineer

13 The Israel Chemist and Engineer Issue 1, September 2015, Tishrei 5776 Scientific Articles NMR of proteins: Eavesdropping on molecular events Jordan Chill Department of Chemistry, Bar Ilan University, Ramat Gan, 52900, Israel Email: Abstract: Proteins owe their amazingly diverse and efficient biological activities to their three-dimensional structure and concerted movements of these structural elements. Therefore,understandingbiologicaleventsonthemolecular level requires a structural viewof proteins. Nuclearmagnetic resonance (NMR) has emerged over the past few decades as a leading method in providing this information, as measureable parameters such as chemical shifts, spin-spin couplings and relaxation rates have been closely correlated to protein structure and dynamics. Using the bacterial potassium channel KcsA as a model system, this article will demonstrate the power of NMR in eavesdropping and reporting on molecular events such as ion conduction, pH- gating and channel-blocking by an inhibitor. Experimental results leading to thesemolecular conclusions arepresented with brief reference to their underlying NMR principles, highlighting the ability of structural NMR methodologies to impact modern biochemical research and drug design. Jordan Chill received his BSc in Chemistry summa cum laude from Tel Aviv University, and his PhD (with distinction) from the Weizmann Institute under supervision of Prof. Jacob Anglister (Structural Biology). His PhD work was awarded the Ester Helinger Excellence Prize. Chill conducted his post-doctoral studies as an EMBO fellow in the laboratory of Dr. Adriaan Bax at the National Institutes of Health (Bethesda, MD, USA) where he studied the structure and function of the KcsA potassium channel using nuclear magnetic resonance (NMR) methods. Since 2007 Chill heads the Biomolecular NMR group at Bar Ilan University, and in 2014 he was appointed Associate Professor. The Chill group employs sophisticated NMR methods complemented by other biophysical approaches to investigate protein structure, protein-protein interactions, membrane-associated proteins and intrinsically disordered proteins, all in the context of biological function, health and disease. Protein structure and dynamics Biological function cannot be imagined without proteins, or polypepetides, polymers composed of the 20 proteogenic α-amino acids. Proteins are responsible for a wide range of cellular tasks and events, including (to name a few) catalysis, recognition, the immune response, transport, cell structure and skeleton, signaling, and neurotransmission. They owe these fascinating capabilities to their three-dimensional structures that create interaction surfaces with unique patterns of charged, polar, and hydrophobic patches. Together, these grant proteins their affinity to ligands and other proteins and ability to perform their function in potent and often highly selective fashion. While structure is not a prerequisite of biological function – indeed, some polypeptides known as intrinsicallydisorderedproteins (IDPs) lack stable structure yet have important biological roles – the two are clearly closely correlated. This accounts for the development of the field of structural biology over the past few decades, emphasizing the structure-function paradigm in understanding proteins and investing extensive research efforts in determining the structure of proteins, typically by X-ray crystallography or by nuclear magnetic resonance (NMR). Also important are protein dynamics, non-random fluctuations in protein structure, which are often at the heart of a biological event; examples of this include the opening/closing of a catalytic site while binding a ligand and conformational changes allowing two proteins two interact. It is clear that a molecular understanding of how proteins fulfill their cellular obligations requires a comprehensive view of protein structure and dynamics. Biomolecular NMR: opportunities and challenges Nuclear magnetic resonance (NMR) is a spectroscopy based on a fundamental physical property of atoms, nuclear spin. When placed in a magnetic field the quantum properties of spins divide them into two populations separated by an energy difference. Since the width of this gap depends upon molecular and electronic structure, the absorption spectrum under magnetic field (in the radio-wave MHz range) reflects the location of the observed nuclei ( prizes/physics/laureates/1952/purcell-lecture.pdf). In the case of proteins, the number of observable nuclei (sometimes thousands) precludes their identification by standard methods. Instead, new methodologies have been developed for proteins, notably isotopic labeling, heteronuclear NMR