A major, six-armed glycoprotein from embryonic cartilage

Area of Science:

• Biochemistry
• Developmental Biology
• Extracellular Matrix Research

Background:

• Hyaline cartilage is a complex tissue containing collagens and glycoproteins.
• The structural roles of many cartilage components are not fully understood.
• Previous studies indicated the presence of novel glycoproteins in embryonic tissues.

Purpose of the Study:

• To isolate and identify a major glycoprotein from chicken embryo sternum cartilage.
• To characterize the structure and properties of this identified glycoprotein.
• To determine if this glycoprotein is related to previously identified antigens.

Main Methods:

• Co-extraction of cartilage components, including collagen types II and IX.
• Polyacrylamide gel electrophoresis (PAGE) for molecular mass determination.
• Rate zonal centrifugation for conformational analysis.
• Immunoblotting using a specific monoclonal antibody (M1).
• Rotary shadowing electron microscopy for structural visualization.

Main Results:

• Isolation of a high molecular mass glycoprotein (>10^6 daltons) from chicken embryo sternum.
• Electrophoretic analysis revealed subunits at 205/195 kd upon reduction.
• Sedimentation analysis indicated a highly extended molecular conformation (13S).
• Immunoblotting confirmed the glycoprotein's identity as myotendinous antigen (MTA).
• Electron microscopy showed an unusual six-armed structure, identical to hexabrachion.
• The M1 antibody decorated these structures, confirming hexabrachion is MTA.

Conclusions:

• Hexabrachion is identified as myotendinous antigen (MTA), a major cartilage glycoprotein.
• MTA possesses a unique, extended, six-armed structure.
• This molecule's structure suggests a role in connecting extracellular components in cartilage.