Three-dimensional structure of an invertebrate intercellular communicating junction.

Area of Science:

• Cell biology
• Structural biology
• Biophysics

Background:

• Gap junctions mediate direct cell-to-cell communication.
• Connexons form channels within gap junctions.
• Arthropod gap junction structures are less characterized than mammalian counterparts.

Purpose of the Study:

• To determine the three-dimensional structure of gap junctions from the American lobster (Homarus americanus) hepatopancreas.
• To characterize the connexon oligomer and its arrangement within the junctional array.
• To compare the structural features with known mammalian gap junctions.

Main Methods:

• Isolation of gap junction arrays from Homarus americanus hepatopancreas.
• Three-dimensional reconstruction using electron microscopy of negatively stained specimens to ~25 Å resolution.
• High-resolution projection imaging of glucose-embedded specimens to ~10 Å resolution.

Main Results:

• Isolated gap junctions exhibited highly ordered, crystalline arrays of hexagonally packed connexons.
• The connexon was identified as an annular oligomer projecting ~30-45 Å from the cytoplasmic surface.
• The extracellular channel region measured approximately 40-45 Å in width, with distinct subunit contrast observed in projection images.

Conclusions:

• The Homarus americanus gap junction structure shares similarities with rat liver junctions but shows differences in stain distribution.
• The findings provide a detailed structural model for arthropod gap junctions.
• This research contributes to understanding the molecular basis of intercellular communication across different animal phyla.