Why endogenous TRPV6 currents are not detectable-what can we learn from bats?

Area of Science:

• Molecular Biology
• Ion Channel Physiology
• Biochemistry

Background:

• Transient Receptor Potential Vanilloid 6 (TRPV6) is a calcium-selective channel with limited detectable currents in native tissues.
• TRPV6 translation initiation in humans and mice uses a non-canonical ACG codon, unlike the canonical AUG in bats.
• The N-terminus and upstream sequences significantly influence TRPV6 channel properties.

Purpose of the Study:

• To investigate the role of the N-terminus in TRPV6 translation regulation.
• To understand the nucleotide differences between human and bat TRPV6 and their impact on translation.
• To explore the functional consequences of altered TRPV6 translation efficiency.

Main Methods:

• Development of human/bat TRPV6 chimeras and mutants.
• Analysis of translational control mechanisms.
• Electrophysiological recordings to assess channel function.
• Investigation of ribosomal scanning and protein synthesis.

Main Results:

• Human TRPV6 sequences downstream of the ACG start codon decelerate ribosomal scanning.
• Stem-loop formation and initiator tRNA binding to ACG likely cause low protein synthesis.
• Bat TRPV6 initiates translation from an AUG codon, suggesting evolutionary adaptation.
• The translational control mechanism can also regulate Green Fluorescent Protein (GFP) expression.

Conclusions:

• TRPV6 translation is regulated by a unique mechanism involving a non-canonical ACG start codon, limiting protein synthesis and preventing calcium overload.
• This translational regulation is likely an adaptation to varying dietary calcium levels, as seen in bats.
• The identified mechanism offers a novel way to control protein expression, applicable to other proteins like GFP.