As a key player in cell adhesion, the glycoprotein fibronectin is involved in the complex mechanobiology of the extracellular matrix. Although the function of many modules in the fibronectin molecule has already been understood, the structure and biological relevance of the C-terminal cross-linked region (CTXL) still remains unclear. It is known that fibronectin is only phosphorylated in the CTXL domain, but no results have been presented to date, which indicate a biological function based on this phosphorylation. For the first time, we introduce a structural model of the CTXL region in fibronectin, which we obtained by exhaustive replica exchange molecular dynamics simulations (TIGER2hs). The sampling revealed a conformational landscape of the dimerization module, and the global minimum state showed an umbrella-like module body and conspicuous structural region with two feet. We observed that the CTXL foot region exhibits a structural stability in its physiological state, which disappears upon changes in the phosphorylation state. Thus, our in silico studies enabled us to show that the flexibility of the CTXL region is guided by phosphorylation. These results indicate an in vivo function of the CTXL domain in protein binding and cell adhesion, which is controlled by phosphorylation.
Fly-by-feel describes how flying animals capture aerodynamic information via their wings' sensory system to implement or enhance flight control. Traditional studies on animal flight emphasized controlling body stability via visual or inertial sensory inputs. In line with this, it has been demonstrated that wing sensory systems can provide inertial state estimation for the body. What about the state estimation of the wings themselves? Little is known about how flying animals utilize their wing sensory systems to monitor the dynamic state of their highly deformable wings. This study is a step toward a comprehensive investigation of how a flying animal senses aerodynamic and aeroelastic features of the wings relevant to flight control. Odonates: dragonflies and damselflies, are a great model for this because they have excellent flight performance and their wing structure has been extensively studied. Here, we developed a strategy to map the entire sensory system of Odonata wings via confocal microscopy. The result is the first complete map of a flying animal's wing sensory system, including both the external sensor morphologies and internal neuroanatomy. This complete search revealed over 750 sensors on each wing for one of the smallest dragonfly species and roughly half for a comparable size damselfly. We found over eight morphological classes of sensors, most of which resembled mechanosensors. Most sensors were innervated by a single neuron with an innervation pattern consistent with minimising wiring length. We further mapped the major veins of 13 Odonate species across 10 families and identified consistent sensor distribution patterns, with sensor count scaling with wing length. To explain the strain sensor density distribution along the major veins, we constructed a high-fidelity finite element model of a dragonfly wing based on micro-CT data. This flapping wing model revealed dynamic strain fields and suggested how increasing sensor count could allow encoding of different wing states. Taken together, the Odonate wing sensory system is well-equipped to implement sophisticated fly-by-feel flight control.
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