STRUCTURE OF A COMPACT PEPTIDE FROM STAPHYLOCOCCAL NUCLEASE DETERMINED BY CIRCULAR-DICHROISM AND NMR-SPECTROSCOPY

Compact regions in proteins are thought to correspond to domains. If this is true, the structure of a compact region excised from a protein should closely resemble the structure in the intact protein. To test this theory, a compact peptide corresponding to residues 129-142 of staphylococcal nuclease (Ac-EAQAKKEKLNIWS-NH2) was synthesized and its solution structure determined using circular dichroism (CD) and 2D NMR. In aqueous solution, the peptide exhibits CD spectra characteristic of a nascent helix. This nascent helical structure is stabilized by the addition of 2,2,2-trifluoroethanol. Under these conditions, the chemical shift indexes of the H-1 alpha and C-13 alpha resonances, temperature coefficients of amide protons, and NOE constraints are all consistent with the peptide's structure being a helix-turn. This structure is almost identical to that found in the intact protein.