Tubular membrane protrusions — filopodia, tunneling nanotubes, retraction fibers — are ubiquitous structures on the cell surface, essential for intercellular communication, wound healing, angiogenesis, and cancer progression. Yet these delicate membrane tubes face a fundamental biophysical paradox: they must be flexible enough to perform dynamic functions, yet robust enough to withstand mechanical forces such as fluid shear stress and cell–matrix adhesion. While the cytoskeleton has long been recognized as the primary structural support for membrane tubules, the contribution of transmembrane proteins has remained largely unexplored. 

In this study, the authors reveal that the four-pass transmembrane protein tetraspanin 7 (TSPAN7) senses membrane curvature and spontaneously polymerizes into a highly ordered helical configuration on tubular membranes. This helical assembly acts as a "transmembrane skeleton" — a structural scaffold embedded within the lipid bilayer itself — that resists shear-force-induced tube narrowing and rupture. The concept of a transmembrane skeleton, operating not beneath but within the membrane, represents a previously unrecognized class of membrane skeletal architecture and opens new avenues for understanding how cells maintain the structural integrity of their most delicate membrane protrusions.

A research team at Saitama University has discovered that calmodulin-binding peptide (CBP) can switch between two distinct target proteins depending on the surrounding metal-ion environment. Specifically, CBP binds calmodulin in the presence of calcium ions but recognizes human midkine in the presence of sodium ions. By combining surface plasmon resonance experiments with AlphaFold 3 structural prediction, the team uncovered a previously unrecognized mechanism of ion-dependent molecular recognition by a naturally occurring peptide. This finding opens new possibilities for peptide-based molecular recognition, diagnostic technologies, and drug discovery.