Abstract
Recently, a few fish proteins have been described with a high homology to B-type lectins of monocotyledonous plants. Because of their mannose binding activity, they have been ascribed a role in innate immunity. By screening various fish venoms for their integrin inhibitory activity, we isolated a homologous protein from the fin stings and skin mucus of the scorpionfish (Scorpaena plumieri). This protein inhibits alpha1beta1 integrin binding to basement membrane collagen IV. By protein chemical and spectroscopic means, we demonstrated that this fish protein, called plumieribetin, is a homotetramer and contains a high content of anti-parallel beta strands, similar to the mannose-binding monocot B-lectins. It lacks both N-linked glycoconjugates and common O-glycan motifs. Despite its B-lectin-like structure, plumieribetin binds to alpha1beta1 integrin irrespective of N-glycosylation, suggesting a direct protein-protein interaction. This interaction is independent of divalent cations. On the cellular level, plumieribetin failed to completely detach hepatocarcinoma HepG2 cells and primary arterial smooth muscle cells from the collagen IV fragment CB3. However, plumieribetin weakened the cell-collagen contacts, reduced cell spreading, and altered the actin cytoskeleton, after the compensating alpha2beta1 integrin was blocked. The integrin inhibiting effect of plumieribetin adds a new function to the B-lectin family, which is known for pathogen defense.
Highlights
A few fish proteins have been described with a high homology to B-type lectins of monocotyledonous plants
By protein chemical and spectroscopic means, we demonstrated that this fish protein, called plumieribetin, is a homotetramer and contains a high content of anti-parallel  strands, similar to the mannose-binding monocot B-lectins
The inhibitory potential on the comparatively low affinity interaction of integrin ␣31 with laminin-332 is worthwhile, it was the exceptional preference of the venom to block the avid ␣11 integrin binding to its collagen ligand to a remarkably higher extent as compared with the other collagen-binding integrin ␣21, which makes us search for the ␣11 integrin-inhibiting component of the S. plumieri venom
Summary
A few fish proteins have been described with a high homology to B-type lectins of monocotyledonous plants. By screening various fish venoms for their integrin inhibitory activity, we isolated a homologous protein from the fin stings and skin mucus of the scorpionfish (Scorpaena plumieri). This protein inhibits ␣11 integrin binding to basement membrane collagen IV.
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