The Chemical Synthesis Program of the Chemistry Division supports Professor Zhongwu Guo of Wayne State University to prepare GPI conjugates of small molecule dyes by chemical synthesis using the para-methoxybenzyl group for permanent hydroxyl protection as well as GPI-fluorescent protein conjugates by enzyme-catalyzed ligation of synthetic GPIs and proteins. The resulting GPI conjugates will be then utilized to study GPI anchorage of proteins to the cell membrane.
This work would improve our skills and tool box for obtaining complex and important biomolecules and advance our fundamental knowledge about how cell surface proteins are attached to the cell membrane, a process that plays a pivotal role in many biological and pathological processes. The proposed work will have a significant impact on the fields of chemistry and biological sciences, including the development of new therapeutic strategies targeting at proteins on the cell surface. This project also helps educate undergraduate and graduate students and train highly demanding experts in the fields of synthetic and carbohydrate chemistry and glycobiology.
Glycosylphosphatidylinositol (GPI) anchors are a family of complex glycolipids that attach surface proteins and glycoproteins onto the cell membrane and play a critical role in various biological events. This project aims at developing practical methods for the synthesis of homogeneous and structurally well-defined GPIs and GPI conjugates that can be utilized to study related biological problems. In this project, we have developed efficient strategies for the chemical synthesis of various GPIs and GPI derivatives. Employing these synthetic strategies, we have prepared a series of fluorescence-labeled GPI derivatives that make GPIs visible on the cell surface to facilitate investigation. Studies on these GPI derivatives have revealed that both the carbohydrate chain and the lipid structure of GPIs have a significant impact on their biophysical and biochemical properties, such as their distribution, orientation and aggregation in the cell membrane. We have developed a new method for the synthesis of GPI-anchored peptides, glycopeptides and proteins through enzyme-catalyzed site-specific coupling of GPIs with peptides, glycopeptides and proteins. We have established that the same enzyme, sortase, can be utilized to prepare macrocyclic peptides/glycopeptides and to decorate liposomes with proteins or other fluorescent labels in a site-specific manner. These results suggest that sortase can have wide applications. The novel synthetic methods mentioned above have greatly facilitated our access to various pure and structurally defined GPI anchors, GPI derivatives, and GPI-anchored peptides, glycopeptids and proteins, which are very difficult to obtain otherwise. Furthermore, these synthetic methods should be widely applicable. Therefore, this research can have an important and broad impact on GPI chemistry and related research. In the meanwhile, synthetic GPIs and GPI conjugates obtained from this project have greatly facilitated various biological studies about GPI anchors and GPI-anchored proteins, such as their behaviors and functions on the cell surface. The results are not only important for our understanding of GPI anchorage and related issues but also have a broad impact on glycobiology and general biology as GPIs and GPI-anchored proteins are involved in various biological processes.
