Identifying Key Structural Interactions in Heparan Sulfate-Protein Complexes

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Project Summary Glycosaminoglycans (GAGs), such as heparan sulfate (HS), are important components of the extracellular matrix of all cells. The extraordinary structural diversity of GAGs enables them to interact with a wide variety of biological molecules, but primarily proteins, to modulate biological processes, such as cell adhesion, tissue repair, coagulation, and immune response, among many others. Additionally, a number of different viruses, including HIV-1, initiate infection of cells by binding to cell surface GAGs. Unfortunately, the diversity of potential binding motifs in GAG sequences has made identification of relevant sequences challenging. In particular, heparan sulfate (HS) is the most structurally diverse, with sixteen unique disaccharide configurations and 256 unique tetrasaccharide configurations. Significant progress has been made in recent years developing libraries of synthetic HS oligomers, allowing for detailed experimental structural studies of HS-protein complexes. Understanding the structural basis of these interactions is key to drug development and the HS binding protein-HS (HSBP-HS) interaction studies to date have been either non-structural or computational. The overall goal of this project is to utilize these recently developed synthetic HS libraries and NMR-based structural models to identify key interactions. HIV-1 p17 will be used for initial studies because it is very important in many stages of the life cycle of HIV-1. Heparan sulfate receptors are known to influence growth factor signaling, cell adhesion, and enzymatic catalysis on human cells. Thus, this interaction may be one of the deciding factors for disease progression in humans infected with HIV-1. In Aim 1, a library of synthetic HS tetrasaccharides will be screened for binding to human immunodeficiency virus type 1 (HIV-1) p17 protein to identify the sequence-specific HS characteristics of the preferred binding oligomers. In Aim 2, the HSBP-HS complexes of both strong and weak binding sequences will be studied via nuclear magnetic resonance (NMR) to model the structure of the complex and identify key interactions for future drug development. After the methodology is established, HS-binding chemokines will be screened in Aim 3 to identify suitable targets for future NMR studies.