Identification and further characterization of the specific cell binding fragment from sponge aggregation factor

Area of Science:

• Marine biology
• Cellular adhesion
• Biochemistry

Background:

• The aggregation factor (AF) from the marine sponge Geodia cydonium mediates cell-cell adhesion.
• Understanding the molecular components of AF is crucial for elucidating sponge aggregation mechanisms.

Purpose of the Study:

• To identify the specific protein responsible for cell binding within the Geodia cydonium aggregation factor.
• To characterize the binding properties and localization of the identified cell-binding molecule.

Main Methods:

• Generation of monoclonal antibodies (McAbs) against the aggregation factor.
• Immunoblotting and immunoprecipitation to identify and isolate the 47-kD protein.
• Binding assays to determine affinity, Ca++ ion dependence, and species specificity.
• Indirect immunofluorescence staining for protein localization.

Main Results:

• McAbs identified a 47-kD protein fragment as the cell-binding component of the AF.
• The 47-kD fragment exhibits high-affinity binding (Ka of 7 X 10(8) M-1) to Geodia cells, independent of Ca++ ions.
• Binding is species-specific and can be inhibited by the aggregation receptor.
• The 47-kD protein is localized extracellularly.

Conclusions:

• The 47-kD protein fragment is identified as the primary cell-binding molecule of the Geodia cydonium aggregation factor.
• This molecule plays a key role in species-specific cell adhesion in marine sponges.
• The findings provide insights into the molecular basis of cell aggregation in invertebrates.