LRP1 is a member of the low density lipoprotein (LDL) receptor family, which plays important and wide-ranging roles in physiological processes as diverse as lipoprotein metabolism, uptake of proteinases and their inhibitor complexes, viral entry, and even early development. These roles can also lead to disease in instances of mutation and absence, with defects in LDLR resulting in hypercholesterolemia, and the LRP1 knockout being embryonically-lethal in mice. LRP1, like all members of the LDLR family, is a mosaic protein composed of multiple copies of ligand-binding (CR domain), EGF-like and 2-propellor (YWTD) domains. For it to function effectively in vivo it must not only fold correctly and be efficiently exported to the cell surface, but must be able to both bind and internalize extracellular ligands and subsequently release them intracellularly for further processing or degradation. Our long term goal is to understand the relationship between the structure of LRP1 and how it functions. This renewal application seeks quantitative answers to these basic questions, and builds on many years'experience examining the ligand-binding CR domains of LRP1 and the structure and properties of the chaperone protein RAP (receptor associated protein). The current proposal is a logical extension of our reductionist approach of examining pair-wise interactions between binding partners, in which we will utilize insight gained previously on studies of small fragments of LRP1 to test ideas on how complete functional regions of the intact receptor work, but includes both in vitro and parallel in vivo studies. We will address the following specific questions. First, does one RAP molecule exploit its three-domain structure to bind extremely tightly in the ER to each ligand-binding cluster of LRP1 and so protect it from premature binding of any other potential ligand? Second, is this same multi- domain high affinity interaction of RAP exploited to promote correct folding of the ligand-binding clusters in the ER? Third, do the YWTD domains that flank each of the ligand binding clusters serve to displace both internalized ligands and RAP by a common competition mechanism at low pH that is made highly efficient by the intramolecular nature of the competing domain?

Public Health Relevance

Atherosclerosis is a major cause of death in the United States. Factors contributing to it include aberrant clearance of serum lipoproteins, and imbalance in the regulation of proteins associated with blood coagulation and inflammation of the artery wall. One of the receptors involved in regulating these processes is LRP1, a member of the low density lipoprotein receptor family. However, the relationship between the structure of LRP1 and how it interacts with the many different proteins involved in these processes is not well understood. Our goal is to advance understanding of the mechanisms whereby LRP1 participates in these systems. Such knowledge could be of great use in designing specific drugs to target different functions of LRP1.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM054414-22
Application #
8588331
Study Section
Hemostasis and Thrombosis Study Section (HT)
Program Officer
Wehrle, Janna P
Project Start
1991-05-01
Project End
2014-11-30
Budget Start
2013-12-01
Budget End
2014-11-30
Support Year
22
Fiscal Year
2014
Total Cost
$310,860
Indirect Cost
$112,860
Name
University of Illinois at Chicago
Department
Biochemistry
Type
Schools of Medicine
DUNS #
098987217
City
Chicago
State
IL
Country
United States
Zip Code
60612
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
Gettins, Peter G W; Olson, Steven T (2016) Inhibitory serpins. New insights into their folding, polymerization, regulation and clearance. Biochem J 473:2273-93
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