Journey of a cold sensor - VAMP7-dependent transport of TRPM8

Ratio of Hydrophobic-Hydrophilic and Positive-Negative Residues at Lipid-Water-Interface Influences Surface Expression and Channel Gating of TRPV1

During evolution, TRPV1 has lost, retained or selected certain residues at Lipid-Water-Interface (LWI) and formed specific patterns there. The ratio of "hydrophobic-hydrophilic" and "positive-negative-charged" residues at the inner LWI remains conserved throughout vertebrate evolution and plays important role in regulating TRPV1 trafficking and localization. Arg575 is an important residue as Arg575Asp mutant has reduced surface expression, co-localization with lipid raft markers, cell area and increased cell lethality. This lethality is most likely due to the disruption of the ratio between positive-negative charges caused by the mutation. Such lethality can be rescued by either using TRPV1-specfic inhibitor 5'-IRTX or by restoring the positive-negative charge ratio at that position, i.e. by introducing Asp576Arg mutation in Arg575Asp backbone. We propose that Arg575Asp mutation confers TRPV1 in a "constitutive-open-like" condition. These findings have broader implication in understanding the molecular evolution of thermo-sensitive ion channels and the micro-environments involved in processes that goes erratic in different diseases. The segment of TRPV1 that is present at the inner lipid-water-interface (LWI) has a specific pattern of amino acid combinations. The overall ratio of +ve charge /-ve charge and the ratio of hydrophobicity/hydrophilicity remain constant throughout the vertebrate evolution (ca 450 million years). This specific pattern is not observed in the outer LWI region of TRPV1.