Outer pore architecture of a Ca2+-selective TRP channel

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Transient Receptor Potential (TRP) channels are crucial cation channels with diverse functions.
• The structural basis for the functional diversity of TRP channels remains largely unknown.
• Detailed structural studies of TRP channel pores are needed to understand their mechanisms.

Purpose of the Study:

• To investigate the pore architecture of TRPV6, a calcium-selective TRP channel.
• To determine the pore dimensions and identify pore-lining residues.
• To develop a structural model for the TRPV6 pore.

Main Methods:

• Cysteine-scanning mutagenesis to probe pore dimensions and identify pore-lining segments.
• Permeability studies using organic cations to estimate pore diameter.
• Reactivity assays with sulfhydryl-reactive reagents (Ag+, MTS reagents) to map pore structure.
• Homology modeling based on the KcsA bacterial potassium channel structure.

Main Results:

• The TRPV6 pore diameter was estimated to be 5.4 Å.
• A mutation in Asp(541) altered the apparent pore diameter, identifying it as part of the narrowest pore region.
• Evidence for a pore helix and a cation-selective filter at the outer pore was obtained.
• A structural model revealed conserved features with K+ channels but a wider selectivity filter in TRPV6.

Conclusions:

• The TRPV6 pore shares structural similarities with K+ channels, including a pore helix and selectivity filter.
• The TRPV6 selectivity filter is wider and lined by amino acid side chains, differing from K+ channels.
• This study provides the first structural model of a TRP channel pore, explaining its properties and diversity.