Solution structure of a naturally-occurring zinc-peptide complex demonstrates that the N-terminal zinc-binding module of the Lasp-1 LIM domain is an independent folding unit

The three-dimensional solution structure of the 1:1 complex between the synthetic peptide ZF-1 and zinc was determined by ¹H NMR spectroscopy. The peptide, initially isolated from pig intestines, is identical in sequence to the 30 N-terminal amino acid residues of the human protein Lasp-1 belonging to the LIM domain protein family. The final set of 20 energy-refined NMR conformers has an average rmsd relative to the mean structure of 0.55 Å for the backbone atoms of residues 3-30. Calculations without zinc atom constraints unambiguously identified Cys 5, Cys 8, His 26, and Cys 29 as the zinc-coordinating residues. LIM domains consist of two sequential zinc- binding modules and the NMR structure of the ZF-1-zinc complex is the first example of a structure of an isolated module. Comparison with the known structures of the N-terminal zinc-binding modules of both the second LIM domain of chicken CRP and rat CRIP with which ZF-1 shares 50% and 43% sequence identity, respectively, supports the notion that the zinc-binding modules of the LIM domain have a conserved structural motif and identifies local regions of structural diversity. The similarities include conserved zinc-coordinating residues, a rubredoxin knuckle involving Cys 5 and Cys 8, and the coordination of the zinc ion by histidine N(δ) in contrast to the more usual coordination by N(ε) observed for other zinc-finger domains. The present structure determination of the ZF-1-zinc complex establishes the N- terminal half of a LIM domain as an independent folding unit. The structural similarities of N- and C-terminal zinc-binding modules of the LIM domains, despite limited sequence identity, lead to the proposal of a single zinc- binding motif in LIM domains. The coordinates are available from the Brookhaven protein data bank, entry 1ZFO.