Initial analysis of the molecular image of pamlin, a sea urchin cell adhesion protein, by transmission electron microscopy.
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.
Omoto
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T
Department of Biophysics, College of Science, Rikkyo University, Tokyo, Japan.
Katow
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H
D000818:Animals; D001704:Biopolymers / Q000737:chemistry; D002118:Calcium / Q000494:pharmacology; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000187:drug effects / Q000648:ultrastructure*; D019281:Dimerization; D008854:Microscopy, Electron; D008958:Models, Molecular; D012617:Sea Urchins / Q000737:chemistry / Q000187:drug effects / Q000648:ultrastructure*
D001704:Biopolymers; D015815:Cell Adhesion Molecules; D002118:Calcium