Role of the transmembrane polar residues on CD151 in cholesterol binding.

Tetraspanins superfamily proteins have been shown to play an important role in several physiological processes and diseases such as cancer. Transmembrane polar residues of tetraspanins have an implication in regulating the process of cancer metastasis. Tetraspanin CD82 has been demonstrated to exert an anti-metastatic role while mutating polar residues in its transmembrane domains (TMDs) abrogates its metastasis inhibitory role. However, CD151, being pro-metastatic tetraspanin, the role of polar residues in TMDs of CD151 in cholesterol binding and its stability has not been investigated. In this study, we employed bioinformatics analysis of CD151 sequences to determine polar residue in TMDs, molecular docking, dynamics, and normal mode analysis studies to investigate the contribution of polar residues on cholesterol binding by modelling and comparing wild type with polar residue mutant of CD151. The study finds three polar residues Asn24, Glu104 and Gln234, in the TMD1, TMD2, and TMD4, respectively, in CD151 that are conserved in most vertebrates indicating their functional significance. Furthermore, we found that these polar residues are required for CD151 stability and facilitate stable interactions with cholesterol. Further cholesterol binding influenced the differences in the distance between large and small extracellular domains of CD151 indicating its important role in the open and closed conformation of the protein. In summary, CD151 exists in open and closed conformation by regulating its interactions with cholesterol. This interaction may modulate the cell membrane dynamics suggesting its potential implication in cancer metastasis.