Using apparent Kd values and dynamic range of biosensors, a parameter introduced in this paper, the length of linker based on a predicted domain can be easily adjusted until the accurate domain responsible for CaM binding is identified. For GPCRs, the submembrane domains are short fragments that allow for easy screening using this approach. Second, biosensors can be expressed and purified with relative ease and cost effectiveness. This is particularly helpful when there are multiple CaM-binding sites in the same protein, as in the case of GPER. Third, since FRET is proportionate to the inverse 6th power of the molecular distance between the donor and acceptor fluorophores, the technique is very sensitive and therefore allows highly quantitative characterization of the interaction between CaM and its binding domains. Fourth, specific CaM binding to the linker sequence only involves changes in the fluorescence intensities of the donor and Rotenone acceptor fluorophores and not any shifts in their spectral peaks, facilitating precise quantitation. Finally, the Ca2+ sensitivity of CaM-target interactions can be measured with high precision using the approach described in this paper. Knowledge of this sensitivity allows prediction of the physiological scenarios that facilitate interactions between CaM and the individual sub-membrane domains of a GPCR. This is particularly true given the constantly trafficking nature of GPCRs through different cellular locales, where the free Ca2+ concentrations may vary substantially. In this study, we have utilized FRET biosensor technique for the first time to demonstrate direct interaction between GPER and CaM and identify four distinct CaM-binding sequences in the submembrane domains of this receptor. The majority of CaM binding domains identified so far in GPCRs are located in either the third submembrane domain or the juxtamembrane section of the fourth. To our knowledge, GPER is the first GPCR identified to possess four CaM-binding domains. Detailed characterizations of biosensor responses indicate that these domains bind Ca2 with significantly different affinities in the sub- to high micromolar ranges. The sensitive nature of the biosensor technique has enabled identification of the role of different fragments in the sequence under study in the interaction with CaM. This clearly indicates an important role of the basic patch 170–175 in CaM binding to SMD2. The apparent Kd values are obtained in vitro on isolated purified biosensors and, like values obtained using synthetic peptides,2-Thenoyltrifluoroacetone are not necessarily the same as in the entire receptor, whose expression and purification remains a challenge. Nevertheless, they provide a useful guide to predict interactions that might occur where GPER resides in its cycle in the cell. TYLCSV is a phloem-limited geminivirus, with a monopartite genome containing six open reading frames, bidirectionally organized in two transcriptional units coding for a coat protein, two proteins related to replication, a movement protein, a transcription activator protein and a pathogenicity factor C4. Several interactions between geminiviral proteins and host factors, able to impact on plant gene expression, are known. For example, Rep interacts with the host retinoblastoma-related protein,which represses the cell cycle progression by its interaction with E2F. The TrAP protein inactivates the adenosine kinase, thus intervening on transcriptional gene silencing.