Cooperative unfolding of distinctive mechanoreceptor domains transduces force into signals.

Lining Ju,Cheng Zhu,Lingzhou Xue,Yunfeng Chen,Xiaoping Du

doi:10.7554/elife.15447

Abstract

How cells sense their mechanical environment and transduce forces into biochemical signals is a crucial yet unresolved question in mechanobiology. Platelets use receptor glycoprotein Ib (GPIb), specifically its α subunit (GPIbα), to signal as they tether and translocate on von Willebrand factor (VWF) of injured arterial surfaces against blood flow. Force elicits catch bonds to slow VWF-GPIbα dissociation and unfolds the GPIbα leucine-rich repeat domain (LRRD) and juxtamembrane mechanosensitive domain (MSD). How these mechanical processes trigger biochemical signals remains unknown. Here we analyze these extracellular events and the resulting intracellular Ca(2+) on a single platelet in real time, revealing that LRRD unfolding intensifies Ca(2+) signal whereas MSD unfolding affects the type of Ca(2+) signal. Therefore, LRRD and MSD are analog and digital force transducers, respectively. The >30 nm macroglycopeptide separating the two domains transmits force on the VWF-GPIbα bond (whose lifetime is prolonged by LRRD unfolding) to the MSD to enhance its unfolding, resulting in unfolding cooperativity at an optimal force. These elements may provide design principles for a generic mechanosensory protein machine.

Highlights

Platelets can serve as a natural model system for studying cell mechanosensing as they rapidly respond to changes in hydrodynamic forces and substrate stiffness due to vascular pathology (Jackson, 2011; Qiu et al, 2015)
This coupled mechanical-biochemical process can be broken down into four steps: 1) Mechanopresentation: the receptor binding domain A1 is exposed by structural changes in von Willebrand factor (VWF) induced by elongational flow and collagen immobilization (Ju et al, 2015a; Springer, 2014); 2) Mechanoreception: glycoprotein Iba (GPIba) leucine-rich repeat domain (LRRD) receives the force signal via engaging VWF-A1 to tether the platelet against shear stress; 3) Mechanotransmission: force is propagated from the LRRD through the mucin-like macroglycopeptide (MP) stalk
In the BFP setup, a probe bead was functionalized with VWF-A1 or an anti-glycoprotein Ib (GPIb) monoclonal antibody to serve as a surrogate subendothelial surface (Figure 1A,B)

Summary

Introduction

Platelets can serve as a natural model system for studying cell mechanosensing as they rapidly respond to changes in hydrodynamic forces and substrate stiffness due to vascular pathology (Jackson, 2011; Qiu et al, 2015). Previous studies have suggested the role of GPIba as a mechanoreceptor, for force exerted on it via its ligand VWF induces platelet signaling (Ruggeri, 2015). This coupled mechanical-biochemical process (mechanosensing) can be broken down into four steps: 1) Mechanopresentation: the receptor binding domain A1 is exposed by structural changes in VWF induced by elongational flow and collagen immobilization (Ju et al, 2015a; Springer, 2014); 2) Mechanoreception: GPIba LRRD receives the force signal via engaging VWF-A1 to tether the platelet against shear stress; 3) Mechanotransmission: force is propagated from the LRRD through the mucin-like macroglycopeptide (MP) stalk (cf Figure 2A) (Fox et al, 1988) and the MSD across the membrane to adaptor and signaling molecules (e.g. 14-3-3z) inside the platelet (cf Figure 7G); and 4) Mechanotransduction: force induces mechano-chemical changes to

Methods

Results

Conclusion