1.A.131. The Putative TRP-like Channel (P-TRPL-Ch) Family
The proteins that comprise this family have been extensively characterized (see references cited for the various (putative) channel proteins in the family), but they are very distantly related (if at all) to other members of the TRP-CC family (TC# 1.A.4). The 1.A.131 family was previously part of the TRP-CC family with TC # 1.A.4.9. Then the great destance between the members of the TRP-CC and P-TRPL-Ch families was revealed, so the P-TRPL-Ch family was assigned its own family number. These proteins are large (~740 aas) with most, but not all, having a large hydrophilic domain with from 0-4 scattered TMSs, followed by 3 TMSs (possibly with a helix-p-loop-helix structure, as the central putative TMS is always the smallest hydrophobicity peak of the three). These three peaks are followed by but separated from four similarly hydrophobic peaks that are likely to be TMSs. Thus, the basic constant region of these proteins is the 3 + 4 C-terminal TMS region. Most members of this family are derived from fungi. These channels may act as ion transporters, transferring Ca2+ from the cytosol into the Golgi apparatus and maintaining cellular calcium homeostasis. Therefore, TrpR appears to function as a Golgi membrane calcium ion channel that is involved in cell wall integration (Wang et al. 2021).
References:
Yeast
TRP-like ion channel PKD2 (Polycystic kidney disease-related ion channel 2). It regulates cytoplasmic calcium ion concentrations (Ma et al. 2011). The functions of Pkd2 include playing roles in cell wall synthesis, membrane protein trafficking and regulating cell separation during cytokinesis (Aydar and Palmer 2009; Morris et al. 2019). The protein has 710 aas and 9 TMSs in a 1 (N-terminus) + 1 (at residue 180) +3 (residues 320 - 420) + 4 (residues 470 - 580).
Yeast
Pkd2 of Schizosaccharomyces pombe
Flavin carrier protein 2, Flc2p. May be responsible for the transport of FAD (and heme) into the endoplasmic reticulum lumen, where FAD may be required for oxidative protein folding involved in disulfide bridge formation (Protchenko et al. 2006).
Yeast
Flc2 of Saccharomyces cerevisiae
Trp-like channel protein of 862 aas and 12 TMSs in a 1 + 1 + 2 + 4 + 4 TMS arrangement. Pkd2 mutations, related to autosomal dominant polycystic kidney disease in humans, localizes to the endoplasmic reticulum and regulates calcium signaling in fission yeast (Koyano et al. 2023).
Fungi
TRP-like channel protein of Schizosaccharomyes pombe (O94543)
Inner membrane TRP Ca2+ channel, TrpR, of 1134 aas and ~9 TMSs. TrpR works as a Golgi membrane calcium ion channel that influences cell wall integration (Wang et al. 2021). It performs important roles in conidiation and in adapting to cell wall disruption reagents in a high temperature-induced defect-dependent manner, especially under calcium-limited culture conditions (Wang et al. 2021).
TrpR of Emericella nidulans (Aspergillus nidulans)
DUF907 domain-containing protein of 794 aas and 7 TMSs in the C-terminal half of the protein and possibly 1 or 2 additional TMSs in the N-terminal half. This protein shows extensive sequence similarity with other members of subfamily 1.A.4.9. It may be the TRP protein described by Guo et al. 2022. The VdASP F2 protein has been reported to regulate the formation of melanized microsclerotia by interacting with VdTRP (Guo et al. 2022).
.
DUF907 protein of Verticillium dahliae
Integral membrane protein of 1180 aas and 10 TMSs in a 1 + 2 + 7 TMS arrangement. It may be the TRP protein examined by Guo et al. 2022.
IMP of Verticillium dahliae
TRP-domain-containing protein of 925 aas and 9 putative TMSs in a 2 + 3 + 4 TMS pattern, where the 3 TMS cluster may be a helix-p-loop- helix channel forming unit. This would be true of all family members.
TRP protein of Annulohypoxylon bovei var. microspora
Putative transient receptor potential ion channel of 781 aas and 9 TMSs in a possible 2 + 3 + 1 + 3 TMS arrangement.
Putative TRP channel of Phaeomoniella chlamydospora