Molecular structure and regulation of the epithelial calcium channels TRPV5 and TRPV6.

Abstract

Ca2+ homeostasis is of utmost importance for the normal development and function of the body. Active transcellular Ca2+ transport involves a chain of Ca2+ transport proteins mediating apical Ca2+ influx, transport to the basolateral membrane and extrusion into the bloodstream. Regulation of the two epithelial Ca2+ channels, TRPV5 and TRPV6 that mediate the rate-limiting cellular Ca2+ entry steps, is pivotal to control the transcellular Ca2+ transport rate. In this respect, elucidation of the mechanisms underlying the molecular structure and regulation of TRPV5 and TRPV6 activity is instrumental to better comprehend the molecular nature of Ca2+ homeostasis. The goal of this thesis was, therefore, to unravel the molecular structure and regulation mechanisms of TRPV5 and TRPV6. By the studies in the present thesis, the assembly motif of TRPV5 forming tetrameric complexes was investigated, two critical assembly domains in the N- and C-tail of TRPV5 were identified. A novel operation mode for channel interacting protein Rab11a in the regulation of TRPV5 and TRPV6 was elucidated. In addition, this study showed for the first time a novel mechanism through which TRPV5 is regulated by the anti-ageing hormone klotho and ŒÂ-glucuronidase. Furthermore, molecular mechanism of hypercalciuria observed in tissue-kallikrein knockout mice was elucidated. Moreover, the study demonstrated the effect of different glycosidase proteins in addition to ŒÂ-glucuronidase and klotho on TRPV5 activity, and a predominantly stimulatory effect of klotho on the epithelial Ca2+ channels TRPV5 and TRPV6 was finally identified.