VHH(dGBP1) is a single-domain antibody fragment, derived by mutagenesis of VHH(GBP1), that binds the GFP fluorescent protein and its derivative YFP. VHH(dGBP1) contains 6 additional amino acid substitutions (A25V, E63V, S73R, S98Y, Q109H, and S117F) compared to VHH(GBP1), resulting in it showing antigen-dependent stability; in the absence of antigen the protein is unstable, while in the presence of antigen (such as GFP or YFP), the VHH(dGBP1) protein is stabilized (PMID:27205882).