A major lesson from eukaryotic genome-sequencing projects is that the absolute number of genes an organism's genome encodes is not the best parameter for defining biological complexity. Instead, the complex functions associated with human health and disease are determined by combinatorial expansion of genomic information in the form of post-translational modifications. Of these, the most ubiquitous is glycosylation, highlighting the importance of glycobiology in the postgenomic era. Our research group is pursuing three major areas: (1) development of chemical tools for profiling the glycome using molecular imaging and mass spectrometry techniques; (2) investigation of the roles of microbial glycoconjugates in pathogenesis, with an emphasis on Mycobacterium tuberculosis; and (3) development of nanoscale tools for biological research.

Chemical Tools for Glycomics Research
Cell surface oligosaccharides are major determinants of cell-cell interactions during development, the immune response, and pathogenic processes such as microbial infection and tumor cell metastasis. The goal of this program is to develop chemical tools for profiling glycans in cells and living organisms and for elucidating their functions with respect to human disease. One such tool is a chemical reporter system for visualizing glycans on cells. We developed two chemical reactions that employ the azide as a bioorthogonal chemical handle. The azide is delivered to specific glycan types via metabolism of synthetic azido sugars. Once incorporated into cellular glycans, the azido sugars can be selectively reacted with probes for detection, enrichment, or visualization. We are applying this technology to proteomic analysis of protein glycosylation, to the identification of glycan tumor and stem cell biomarkers, and to noninvasive imaging of glycosylation changes during development and disease progression.

A second component of this program is the development of tools for probing changes in protein glycosylation that are associated with disease. We have developed a technique for labeling glycoproteins from serum or tissue samples with isotopically unique probes that enable their rapid detection from complex mixtures by mass spectrometry. We are applying this technology to the identification of novel cancer biomarkers.

Mycobacterial Metabolites Involved in Pathogenesis
Mycobacterium tuberculosis, the causative agent of tuberculosis, is responsible for around 3 million deaths per year. Current treatment protocols are lengthy and complicated, and multidrug-resistant strains have arisen in recent years that remain impossible to treat. Mycobacteria have many unusual features, including a complex cell wall structure comprising sulfated trehalose metabolites that are thought to mediate host-pathogen interactions. We are interested in the biological activities of these metabolites and their biosynthetic origin inside the bacterial cell, with an eye for identifying new avenues for drug development. Toward this end, we are disrupting the genes that encode key biosynthetic enzymes, analyzing their phenotypes in mouse models of tuberculosis, and screening compound libraries for inhibitor leads. We are also pursuing x-ray crystal structures of the most promising enzyme targets.

Nanoscale Tools for Biological Research
Surface-layer (S-layer) proteins self-assemble into two-dimensional arrays with nanoscale periodicity on the surface of various bacterial species. These protein architectures can be induced to form similar structures on synthetic surfaces, including supported lipid bilayers, where we can use scanning probe techniques to study the dynamics of assembly. We are probing the S-layer assembly process by AFM (atomic force microscopy), in conjunction with genetic engineering techniques. Applications of S-layers to device fabrication are also under investigation.