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Initial analysis of the molecular image of pamlin, a sea urchin cell adhesion protein, by transmission electron
Abstract:
Pamlin, an important extracellular protein required early for sea urchin embryogenesis, is readily isolated from the embryos of Hemicentrotus pulcherrimus. A molecular image analysis of pamlin was conducted using immuno-electron microscopy, rotary shadowing and negative staining technique-applied electron microscopy. The electron microscopy showed that a monoclonal antibody to the pamlin alpha-subunit bound to a position 13.5 nm from one end of a purified 255 kDa pamlin molecule, which is a 132 nm long and 6.8 nm wide linear structure. The pamlin structure is composed of three subunits, a 47 nm long 52 kDa alpha-subunit that attaches to one end of a 105 nm long 180 kDa beta-subunit, and a 15.6 nm diameter globular 23 kDa gamma-subunit that binds to the middle of the beta-subunit. The alpha- and beta-subunits together form a 125-140nm linear structure. Intermolecular aggregation frequently occurred between the free end of two beta-subunits of the alphabetagamma pamlin molecule, leaving the entire alpha-subunit surface free. Occasionally associations between the ends of alpha-subunits, or between an alpha-subunit and the middle of a beta-subunit also occurred, but no aggregations of pamlin formed through the gamma-subunit. These homophilic molecular aggregations of pamlin formed a large supramolecular network. In addition, the single pamlin molecule rounded at one end under high calcium ion concentration to form a 'loop', suggesting the presence of a calcium sensitive region in the molecule.
Insights
Pamlin, an essential protein for sea urchin development, forms a supramolecular network through homophilic aggregation. Its structure, composed of alpha, beta, and gamma subunits, exhibits calcium-sensitive properties.
Area of Science:
- Developmental Biology
- Molecular Biology
- Structural Biology
Background:
- Pamlin is a crucial extracellular protein for early sea urchin embryogenesis.
- Understanding pamlin's molecular structure is key to deciphering its developmental role.
Purpose of the Study:
- To elucidate the molecular structure and aggregation properties of pamlin.
- To investigate the role of different subunits in pamlin's supramolecular organization.
- To explore potential calcium-sensitive regions within the pamlin molecule.
Main Methods:
- Immuno-electron microscopy was employed for molecular imaging.
- Rotary shadowing and negative staining techniques were utilized.
- Monoclonal antibodies were used to map subunit positions.
Main Results:
- Pamlin is a 132 nm long, 6.8 nm wide linear molecule (255 kDa) with alpha (52 kDa), beta (180 kDa), and gamma (23 kDa) subunits.
- Alpha and beta subunits form a linear structure (125-140 nm); gamma is globular.
- Homophilic aggregation occurs primarily between beta-subunits, forming a supramolecular network; calcium ions induce a loop formation.
Conclusions:
- Pamlin's distinct subunit composition dictates its linear structure and aggregation behavior.
- The formation of a supramolecular network via beta-subunit aggregation is crucial for its function.
- A calcium-sensitive region exists in pamlin, influencing its conformation.