Membrane and membrane protein dynamics studied with time-resolved infrared spectroscopy

Abstract

Proteins are the machinery of the cell, performing functions essential for life. Proteins do not operate in isolation, however. Their function is intimately coupled to their environment; changes in this environment modulate the behavior of the protein. One of the most striking examples of protein-environment coupling is the interaction between membrane proteins and membranes. These interactions govern some of the most fundamental processes in biology, yet the origins of protein-membrane coupling are not well understood. Infrared (IR) spectroscopy offers a route to non-invasively probing these interactions. However, despite sustained interest in the problem over many decades, only limited progress has been made using IR spectroscopy to study protein-membrane interactions. One of the main reasons for this is the density of information encoded into a small frequency range - many hundreds of oscillators may contribute to a signal which spans a <100 cm-¹ range. This spectral congestion may be relieved by spreading the information over an additional axis - an additional frequency axis in the case of multidimensional IR spectroscopy, or over a kinetic axis in transient relaxation experiments. The temporal information encoded by multidimensional IR spectroscopy and transient experiments also provides a route to studying the dynamics of membranes and membrane proteins over a range of timescales, from sub-picoseconds to milliseconds. The combination of structural and temporal information afforded by IR spectroscopy offers the possibility of developing a truly dynamic picture of membranes and membrane proteins. This thesis details efforts to first develop an understanding of what information is contained within the IR spectrum of biologically-native carbonyl groups, and then use this understanding to develop a picture of what fluctuations occur in membranes on the sub-nanosecond, sub-nanometer time- and length-scales. Interactions between membranes and membrane proteins are probed further by utilizing a rapid temperature-jump to induce a phase transition in the membrane. The response of the membrane, and membrane protein, to this phase transition reveals a picture of conformational change in a membrane protein slaved to the dynamics of the membrane.