The long term goals of this proposal are to understand the structure and function of human alpha-2- macroglobulin (a2M), a pan-proteinase inhibitor and binder of growth factors and its receptor LRP.
Four specific aims are proposed, two directed at understanding the specificity of binding of a2M and the receptor associated protein (RAP) to LRP, and two directed at understanding structural features of a2M that enable it to undergo proteinase-induced activation to a receptor-recognized species. A range of structural approaches that are currently used in the lab will be employed, including high resolution NMR and fluorescence spectroscopies, isothermal titration calorimetry and analytical ultracentrifugation (AU) applied to well-defined domains of the proteins of interest and to their complexes.
Aim 1. To determine the atomic interactions involved in recognition of a2M by LRP. The structure of the receptor binding domain (RED) of a2M and a pair of complement-like repeats (CR3-CR4) from LRP to which it binds with high affinity will be determined by NMR spectroscopy. The role of specific contact residues in determining affinity and specificity will be analysed by mutagenesis and characterization of the binding by ITC.
Aim 2. To determine the basis for RAP's ability to bind to LRP. Fluorescence resonance energy transfer between exogenously-introduced acceptor fluorophores and endogenous tryptophans will be used to map the organization of the three domains present in RAP and the changes that occur when RAP binds to LRP.
Aims 3 and 4 will test the hypothesis that c^M is composed of discrete domains that have specific functions.
Aim 3 will determine the domain organization of the C-terminal half of ?2M. Predicted domains of o.2M that contain the thiol ester and the growth factor binding region will be expressed and characterized structurally using spectroscopic and calorimetric approaches. This will include examination of the link between the thiol ester forming residues abd the conformation of the thiol ester domain. The nature and function of the remaining parts of the C- terminal half of a2M that may serve as linkers will also be examined.
Aim 4. The role of domain-domain interactions and conformational changes in thiol ester stabilization and cleavage and in receptor binding domain exposure will be determined. The interactions of domains identified in aim 3, as well as the RED will be examined by thermodynamic and spectroscopic approaches with the goal of understanding the nature of the activating signal that exposes RED and promotes thiol ester cleavage Tryptophan variants of intact a2M will enable fluorescence to be used to map domain reorganizations upon activation of the a2M.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Hemostasis and Thrombosis Study Section (HT)
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Wehrle, Janna P
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University of Illinois at Chicago
Schools of Medicine
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Gettins, Peter G W; Olson, Steven T (2016) Inhibitory serpins. New insights into their folding, polymerization, regulation and clearance. Biochem J 473:2273-93
Gettins, Peter G W; Dolmer, Klavs (2016) The High Affinity Binding Site on Plasminogen Activator Inhibitor-1 (PAI-1) for the Low Density Lipoprotein Receptor-related Protein (LRP1) Is Composed of Four Basic Residues. J Biol Chem 291:800-12
Dolmer, Klavs; Campos, Andres; Gettins, Peter G W (2013) Quantitative dissection of the binding contributions of ligand lysines of the receptor-associated protein (RAP) to the low density lipoprotein receptor-related protein (LRP1). J Biol Chem 288:24081-90
Gettins, Peter G W; Dolmer, Klavs (2012) A proximal pair of positive charges provides the dominant ligand-binding contribution to complement-like domains from the LRP (low-density lipoprotein receptor-related protein). Biochem J 443:65-73
Jensen, Jan K; Dolmer, Klavs; Gettins, Peter G W (2009) Specificity of binding of the low density lipoprotein receptor-related protein to different conformational states of the clade E serpins plasminogen activator inhibitor-1 and proteinase nexin-1. J Biol Chem 284:17989-97
Jensen, Jan K; Dolmer, Klavs; Schar, Christine et al. (2009) Receptor-associated protein (RAP) has two high-affinity binding sites for the low-density lipoprotein receptor-related protein (LRP): consequences for the chaperone functions of RAP. Biochem J 421:273-82
Doan, Ninh; Gettins, Peter G W (2008) alpha-Macroglobulins are present in some gram-negative bacteria: characterization of the alpha2-macroglobulin from Escherichia coli. J Biol Chem 283:28747-56