Functional characterization of a naturally occurring Cx50 truncation

Area of Science:

• Cell Biology
• Biophysics
• Ophthalmology

Background:

• Lens fiber maturation involves proteolytic cleavage of connexin 50 (Cx50) C termini.
• The functional impact of this Cx50 truncation on channel properties remains largely unknown.
• Previous studies suggest a correlation between C-terminal cleavage and altered channel gating.

Purpose of the Study:

• To investigate the functional consequences of Cx50 C-terminal truncation.
• To characterize the properties of truncated Cx50 (Cx50tr) channels.
• To elucidate the role of Cx50 truncation in lens fiber maturation and junctional coupling.

Main Methods:

• Expressed truncated murine and human Cx50 (Cx50tr290/294) in Xenopus oocytes and mammalian cells.
• Evaluated protein expression using immunocytochemistry.
• Analyzed channel properties via dual whole-cell voltage clamp, including macroscopic/single-channel conductance, voltage-gating, kinetics, and pH sensitivity.

Main Results:

• Cx50tr290 channels showed an 86-89% reduction in macroscopic conductance compared to full-length Cx50.
• Truncation did not alter single-channel conductance, gating kinetics, or voltage-gating properties.
• Truncated and full-length Cx50 channels exhibited reversible block by cytoplasmic acidification.

Conclusions:

• C-terminal truncation of Cx50 significantly decreases channel conductance but does not inhibit channel formation.
• The observed reduction in conductance is independent of changes in voltage-gating, kinetics, or chemical gating.
• These findings offer a mechanistic explanation for the reduced junctional coupling during lens fiber maturation.