| dc.description.abstract | Glycans play an essential role in biological processes, but our knowledge of their structure and function is limited as compared to other biological molecules. Glycan structure is highly variable. In vivo, glycan structure is determined by enzymes that synthesize, transfer, and cleave monosaccharides. Misregulation of any of these glycan processing steps can lead to human disease. For example, mutations in many types of cancer perturb glycoprocessing pathways. This can lead to overrepresentation of glycans on cancer cells, which help to evade the immune system. To better understand the efficacy of targeting sialoglycans for cancer and to provide improved tools for cancer detection, probes specific for these glycans are needed. Instead of relying on nonspecific antibodies or unstable mammalian and viral glycan binding proteins as probe scaffolds, we can use bacterial proteins with native glycan binding properties. Many bacterial GBPs have been well characterized both structurally and biochemically. To understand more about how bacterial adhesins recognize sialic acid, I crystallized the binding region of a serine rich repeat adhesin from Streptococcus sanguinis strain SK1. This adhesin is particularly interesting for its slightly less common sialic acid recognition motif as well as its tandem Siglec domains. Through structural analysis I determined both Siglec domains are capable of binding glycans. Additionally, some noncanonical motifs bind sialic acid similarly to canonical ones. To better encompass the diversity in amino acid sequence of the sialic acid recognition motif, I redefined the motif from YTRY to ФTRX. Additional research engineering these Siglec-like binding regions from streptococcal adhesins to selectively bind α2,3 sialoglycans demonstrates feasibility for developing bacterial GBPs into selective probes. This same principal can be used to develop probes for α2,6 sialoglycans such as sTn. To my knowledge, there do not exist any naturally occurring lectins that bind α2,6 sialoglycans that can be repurposed as probes. Instead, of using a binding protein, an enzyme can be used. Here, I structurally and biochemically characterize a catalytically inactive mutant of the α2,6 sialyltransferase from Pasteurella multocida. | |
