In nature, proteins are biology's workhorses. These large molecules are made of chains of amino acids and have numerous functions. For instance, producers make it possible for our bodies to metabolize nutrients, water, and oxygen and convert them into life-supporting energy. DNA requires proteins to replicate and transmit genetic information. The antibodies that protect our cells from bacteria and viruses are proteins. And these multifaceted molecules make it possible for cells to communicate vital physiological information with one another, an evolutionary innovation essential to complex organisms like us.
That proteins are so critical to life has made them a hot topic of research since the mid-19th century. Recently, however, advances in science and technology have revolutionized the way scientists study proteins. Many of these new technologies are now available to PSU and Oregon Health and Sciences University (OHSU) researchers working at the Robertson Life Sciences Building (RLSB).
Steve Reichow, Assistant Professor of Chemistry, came to PSU from the Howard Hughes Medical Institute. His research interests lie in exploring proteins and pushing molecular biology boundaries towards new frontiers that will increase our understanding of how and why specific proteins do what they do.
Reichow and his students pursue their research using the RLSB's onsite, state of the art microscopy suite at the OHSU FEI Living Lab. In it, Reichow will study proteins, characterizing their chemical compositions, determining their molecular architecture, and examining the relationships between the intricate structures that give them their distinct shape and the function they perform.
"This is a structural biology lab," Reichow said. "And what we do here is look at the form and function of membrane proteins that perform tasks such as regulating the flow of water or the passage of chemical information through openings in the cell membrane, the lipid bilayer that separates a cell from its environment."
Membrane proteins interact with the lipid bilayers that surround and protect cells. They are gatekeepers of cells, opening, and closing channels through which molecules and chemical information pass through to enter the cell's interior.
Membrane proteins are biologically crucial for several reasons. They allow specific molecules to enter the cell while blocking others. They also permit communication between cells. For example, suppose a particular part of the body requires nutrients, water, or oxygen. In that case, the cells can relay that information to other cells through channels controlled by membrane proteins, thus providing direct resources to where they are needed. Medical science is interested in these proteins because, as the gatekeepers of cells, they may provide paths through which small-molecule drugs could pass in cellular diseases' targeted treatment. Reichow's research aims to unearth the unknown structures and genetic information responsible for membrane proteins' unique properties.
According to Reichow, the work he does in the lab is not dissimilar from the work archaeologists do in the field. "Sometimes you find something, and you're not sure what it is," he said. "But you might be able to look at it and infer what its function might be based on its appearance and composition.
"So an archaeologist might find an object shaped like a bowl and hypothesize that it was used to hold something. We do much the same with proteins, but unlike the archaeologist, we can use the tools available to us to design experiments to test our hypothesis."
The tools Reichow refers to are those of electron microscopy and electron cryo-microscopy (cryoEM) in particular. Because the electron beam's wavelength is so small, electron microscopes can achieve magnifications many thousands of times greater than standard light microscopes. These machines provide superb images of materials such as crystals and metals at the atomic scale. This hasn't been the case for biological samples, sensitive to the harsh conditions within electron microscopes. So until recently, scientists like Reichow relied on X-ray crystallography in which biological samples are crystalized and imaged using an X-ray beam. This method of imaging, however, presents its challenges.
As Reichow explained, now that the techniques of cryoEM have been sufficiently refined and improved, digital imaging technologies have been developed. They are available at the FEI Living Lab, where he can visualize protein structures with much greater detail than has ever been possible. He can freeze biological samples containing proteins to the temperature of liquid nitrogen, preserving the delicate specimen in its natural environment. New direct electron detectors provide pictures, or "movies" with unprecedented resolution. Computers then combine all the data into a single image – allowing him to directly visualize the protein's three-dimensional structure at the level of its amino acid composition. This is the same "atomic-level" detail obtained by X-ray crystallography but without the need to coax the protein into forming a crystal, which is particularly challenging for membrane proteins.
Reichow will use cryoEM and other methods to study a particular class of membrane proteins called Aquaporins. Aquaporins are selective about what they will allow to pass into cells. As their name suggests, they let water into cells, but not other substances such as solutes or ions. One of the Reichow Lab aims is to understand how the flow of water is regulated by cells to meet the physiological needs of our bodies. Another aim is to understand how cells communicate through pathways controlled by membrane proteins, a function essential to several physiological activities, including synchronizing heart muscle contractions, coordination of brain activity, and the sharing of metabolic information.
"In biology, molecular structures play a significant role in the function of how molecules in our bodywork," Reichow said. "The reason I'm so excited to be at PSU is that the FEI Lab is going to allow us to collect better data on these membrane proteins. That is a game-changer for us.
"We're going to be able to construct three-dimensional models and see more detail than ever before. We'll be able to look at these structures at the genetic level. Back in the lab, we can design experiments to see how the function of the proteins changes when we change the form.
"Conversely, if a patient shows up with a disease and we can track that disease to a mutation in a specific protein, pharmaceutical companies may then be able to develop drugs based on the protein's unique structure that target affected cells with those mutant proteins."
According to Reichow, understanding membrane proteins, their form, and how it relates to their function is the primary goal of his research and his future work in the lab. It may lead to improved knowledge of how cells operate and communicate with the rest of the body and play an essential role in how doctors treat disease in the future.