Zinc-mediated helix capping in a triple-helical protein.
Specific sequence signals at alpha-helix termini can assist protein folding by punctuating and cueing secondary structural elements in the final native conformation. Here we report the crystallization of a 56-residue alanine-containing peptide, denoted Ala-10(56), in the presence of Zn(2+). The 1.7 A crystal structure shows that Ala-10(56) forms a parallel trimeric coiled coil with three zinc ions anchoring distinct capping conformations at the amino-terminal ends of the three helices. In each polypeptide chain, the free alpha-amino nitrogen and carbonyl oxygen of the amino-terminal Ser residue coordinate to a Zn(2+) ion to form a five-membered chelate, and the syn-unidentate interaction of the Asp7 side chain with the Zn(2+) cation leads to the formation of a unique docking arrangement for helix capping. Moreover, the coordination of the zinc ion involves a neighboring trimer molecule in the crystal. Consequently, the crystal contacts are stabilized by carboxylate-Zn(2+) interactions between four Ala-10(56) trimers in the crystal lattice. The observed synergy between the protein-zinc ion recognition and the helix-packing arrangements would contribute to the conformational specificity of the Ala-10(56) trimer.
Liu
Jie
J
Department of Biochemistry, Weill Medical College of Cornell University, New York, New York 10021, USA.
Dai
Jiayin
J
Lu
Min
M
D000595:Amino Acid Sequence; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D066298:In Vitro Techniques; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D055672:Static Electricity; D015032:Zinc / Q000737:chemistry*
D008024:Ligands; D011506:Proteins; D015032:Zinc