spGFP11 is an engineered split fluorescent protein fragment (RDHMVLHEYVNAAGIT) derived from the naturally occurring fluorescent protein encoded by the Aequorea victoria GFP gene; it is a small fragment encoding the 11th strand of the GFP β-barrel structure (the spGFP11 sequence corresponds to GFP amino acid residues 215-230, with the additional mutations L221H, F223Y and T225N). If the spGFP11 split fluorescent fragment is brought together with a complementary split fluorescent fragment (e.g. spGFP1-10) in vivo, a functional fluorescent protein may be reconstituted (PMID:15580262). spGFP11 can be used in the 'GFP Reconstitution Across Synaptic Partners' (GRASP) technique (PMID:18255029), to study connectivity in the nervous system.