Studying Subunit Interaction and Complex Assembly of TRP Channels

Excerpt

Transient receptor potential (TRP) proteins serve as subunits in diverse cation channel complexes. These signaling units are typically composed of scaffolds, adaptors, regulatory subunits, and enzymes (for review, see Refs. 1 and 2). The functional core unit within these complexes is a homo- or hetero-oligomeric TRP pore assembly that is likely to contain the essential structures for channel gating and regulation. The obvious structural similarities between TRP- and voltage-gated K⁺ channel proteins have promoted the view of a tetrameric TRP pore complex,^, and this concept has been confirmed experimentally.^, Tight protein–protein interactions between the pore-forming, transmembrane subunits determine the biophysical and regulatory properties of the TRP cation conductances and are thus essential determinants of the (patho)physiological role of individual signal complexes. Communication and cross-talk of the oligomeric TRP pore assemblies with auxiliary proteins such as adaptors, scaffolds, and regulators appear to involve a highly diverse array of molecular interactions, ranging from tight physical association to rather loose and dynamic interactions.^, Both qualitative composition and stoichiometry of cation channel complexes containing a certain TRP protein are most likely dependent on the cellular host environment, as well as the cell phenotype. Our current incomplete understanding of the (patho)physiological function of many TRP proteins is partly due to the lack of information on multimeric assembly and complex composition in native cellular environments, and the difficulties to assign a certain signaling process in native cells to a defined TRP complex arrangement. Therefore, in-depth analysis of the composition of native TRP complexes and identification of the molecular structures and mechanisms of protein–protein interaction within functional TRP signalosomes is prerequisite for understanding the (patho)physiological impact of these structures and for uncovering their potential as therapeutic targets. Because of the remarkable plasticity of functional TRP complexes based on dynamic cellular trafficking and complex rearrangement,^, this task is exceptionally challenging. Successful strategies will require refined classical biochemical, biophysical, and functional measurements complemented by cutting-edge proteome analysis. In the following, we will address the potentials as well as pitfalls and limitations of individual approaches with respect to certain aspects of the TRP complex analysis. Focus will be placed on the advantages and pitfalls of established methods complemented by a brief outline of alternative and novel techniques. Technical requirements and problems will be discussed for analysis of pore complex interactions, as well as regulatory and/or targeting interactions including standard step-by-step working procedures for key methods.