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.