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Characterization of an Extensive Interface on Vitronectin for Binding to Plasminogen Activator Inhibitor-1: Adoption of Structure in an Intrinsically Disordered Region
journal contribution
posted on 2019-12-13, 21:44 authored by Letitia
O. Puster, Christopher B. Stanley, Vladimir N. Uversky, Joseph E. Curtis, Susan Krueger, Yuzhuo Chu, Cynthia B. PetersonSmall-angle neutron scattering (SANS) measurements were
pursued
to study human vitronectin, a protein found in tissues and the circulation
that regulates cell adhesion/migration and proteolytic cascades that
govern hemostasis and pericellular proteolysis. Many of these functions
occur via interactions with its binding partner, plasminogen activator
inhibitor-1 (PAI-1), the chief inhibitor of proteases that lyse and
activate plasminogen. We focused on a region of vitronectin that remains
uncharacterized from previous X-ray scattering, nuclear magnetic resonance,
and computational modeling approaches and which we propose is involved
in binding to PAI-1. This region, which bridges the N-terminal somatomedin
B (SMB) domain with a large central β-propeller domain of vitronectin,
appears unstructured and has characteristics of an intrinsically disordered
domain (IDD). The effect of osmolytes was evaluated using circular
dichroism and SANS to explore the potential of the IDD to undergo
a disorder-to-order transition. The results suggest that the IDD favors
a more ordered structure under osmotic pressure; SANS shows a smaller
radius of gyration (Rg) and a more compact
fold of the IDD upon addition of osmolytes. To test whether PAI-1
binding is also coupled to folding within the IDD structure, a set
of SANS experiments with contrast variation were performed on the
complex of PAI-1 with a vitronectin fragment corresponding to the
N-terminal 130 amino acids (denoted the SMB-IDD because it contains
the SMB domain and IDD in linear sequence). Analysis of the SANS data
using the Ensemble Optimization Method confirms that the SMB-IDD adopts
a more compact configuration when bound to PAI-1. Calculated structures
for the PAI-1:SMB-IDD complex suggest that the IDD provides an interaction
surface outside of the primary PAI-1-binding site located within the
SMB domain; this binding is proposed to lead to the assembly of higher-order
structures of vitronectin and PAI-1 commonly found in tissues.