| Abstract
| - The structure of a 22 amino acid peptide, TPPI [Nedved, M. L.,Gottlieb, P. A., & Moe, G.R. (1994) Nucleic Acids Res.22, 5024−5030],that is similar to the proline repeat segment of thereplicationarrest protein, Tus, has been determined by 1H NMR in 50%trifluroethanol. The structure is a novelleft-handed helix having 5.56 residues per turn and a regular hydrogenbonding network that is limited toone side of the helix and contains a channel that runs down the helixaxis. The latter feature gives thestructure an overall pipe-like appearance; hence, the structure hasbeen designated a proline pipe helix.The Tus proline pipe is also amphiphilic with one side consistingof proline and other nonpolar residueswhile the other side contains mostly basic and other polar residues.Tus and several other proteins thatcontain a similar proline repeat sequence are DNA binding proteins.It is shown here that the prolinepipe helix of TPPI can be accommodated within the major grove of B-formDNA in a manner that positionsnearly all of the basic residues near phosphate groups in the DNAbackbone. The proline pipe helicalmotif may be a structural element of many other proteins includingintegral membrane receptor proteins.
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