A second form of collagenous lectin from the tunicate, Styela plicata

This study characterised a 90 kDa lectin from an invertebrate chordate, the tunicate Styela plicata. One- and two-dimensional electrophoresis showed that the apparent molecular weight of this protein is maintained under both reducing and non-reducing conditions, suggesting that its native form is a monomer. The 90 kDa lectin was localised within a single type of hemocyte (morula cells), but was secreted from those cells when tunicates were challenged with the inflammatory elicitor, zymosan. Functional studies showed that the 90 kDa protein binds to galactose-based sugars in a divalent cation-dependent manner. Amino acid composition analysis and N-terminal amino acid sequencing indicated that the 90 kDa lectin is related to a previously characterised, collagenous lectin from S. plicata, splic43. However, peptide mass fingerprinting identified numerous differences between the two proteins. This suggests that the 90 kDa molecule represents a novel protein that is involved in host defence.