The structural characterization of three membrane associated proteins: Nogo66, Cryptdin-3, and the cytoplasmic tail of JSRV

The study of membrane proteins is essential in biology as they often determine how a cell interacts with the surrounding environment. Membrane proteins fall into two classes, integral and associated. In the dissertation, I will discuss the structural characterization of three different membrane associated peptides, namely Nogo66, Cryptdin3, and the cytoplasmic tail of JSRV. The structural characterization was carried out using Nuclear Magnetic Resonance (NMR), and circular dichroism (CD).;The Nogo66 peptide is an extracellular portion of a larger transmembrane protein. This protein is implicated in axonal collapse in the central nervous system. By studying the structure and dynamics of Nogo66 in a membrane mimetic, we have determined possible modes of interaction with the Nogo receptor. These data include initial binding assays and the overall conformation of Nogo66.;Cryptdin-3 is an antimicrobial peptide expressed in the gut of mice. Cryptdin-3 has been shown to form pores in membranes. As part of the innate immune system antimicrobial peptides play an important role in fighting disease as a first defense against microbes. Several other cryptdins have been characterized, each with effects on bacteria and viruses. By studying Cryptdin-3, I have shown the protein's possible modes of action against microbes.;The last protein studied here is the cytoplasmic tail (CT) of a Jaagsiekte sheep retrovirus (JSRV) protein. This peptide has been implicated in the transforming ability of JSRV on mammalian cells. As such, its study is important in determining the progression of cancer in infected subjects.;In the following chapters, I show that both Nogo66 and the CT of JSRV are unfolded or dynamic in solution. Upon addition of an environment approximating that of the cell, both adopt stable helical conformations. My early structure determination of Cryptdin-3 shows that it has a localization of basic residues, which may be involved in interacting with negatively charged membranes. Overall, the following chapters characterize the structure of the aforementioned proteins. The structure of these peptides leads to potential mechanisms by which they may function.