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 th e synthetic peptide ZF-1 and zinc was determined by H-1 NMR spectrosco py. The peptide, initially isolated from pig intestines, is identical in sequence to the 30 N-terminal amino acid residues of the human prot ein Lasp-1 belonging to the LIM domain protein family. The final set o f 20 energy-refined NMR conformers has an average rmsd relative to the mean structure of 0.55 Angstrom for the backbone atoms of residues 3- 30, Calculations without zinc atom constraints unambiguously identifie d 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 struct ure of an isolated module. Comparison with the known structures of the N-terminal zinc-binding modules of both the second LIM domain of chic ken CRP and rat GRIP with which ZF-1 shares 50% and 43% sequence ident ity, respectively, supports the notion that the zinc-binding modules o f the LIM domain have a conserved structural motif and identifies loca l regions of structural diversity. The similarities include conserved zinc-coordinating residues, a rubredoxin knuckle involving Cys 5 and C ys 8, and the coordination of the zinc ion by histidine N-delta in con trast to the more usual coordination by N-epsilon observed for other z inc-finger domains, The present structure determination of the ZF-1(-) zinc complex establishes the N-terminal half of a LIM domain as an ind ependent folding unit. The structural similarities of N- and C-termina l zinc-binding modules of the LIM domains, despite limited sequence id entity, lead to the proposal of a single zinc-binding motif in LIM dom ains. The coordinates are available from the Brookhaven protein data b ank, entry 1ZFO.