Novel insights into the structure and transport mechanisms of TAPT1

Transmembrane anterior-posterior transformation protein 1 (TAPT1), encoded by the TAPT1 gene expressed in the basal ciliary body, plays a crucial role in cilia formation as well as axial skeletal patterning. Mutations in this gene have been reported to cause several ciliopathies and osteo-related diseases. Unfortunately, the cellular and molecular pathogenic mechanisms are still unclear also due to the lack of X-ray crystallographic structure and further characterization of TAPT1 protein. In this study, we attempted to characterize this protein by in silico techniques. A 3D structure of TAPT1 was generated by the ab initio method, which was further used for the analysis of the substrate-binding site, to determine pore size and for the prediction of the possible substrate(s). Validation by using different software packages revealed a reliable 3D model of TAPT1. Topology modeling revealed that TAPT1 has eight transmembrane helices with a total number of 27 helices in secondary structure. The amino acid residues H235, R323, K443, N446, S447, L450, K453, S454, Y457, K511, N513, D533, K535, D536, and T538 were found to form the pore surface as well as involved in the binding interaction with the substrate(s). This study predicted flavonoids as the possible substrate for TAPT1, which could further be confirmed by ingenuity pathway analysis. Moreover, our analysis indicated that TAPT1 might localize in the mitochondrial membrane in addition to the ciliary basal body. Our study gives novel insights for TAPT1 structure and its function.