PROLINE PIPE HELIX - STRUCTURE OF THE TUS PROLINE REPEAT DETERMINED BY H-1-NMR

The structure of a 22 amino acid peptide, TPPI [Nedved, M. L., Gottlie b, P.A., & Moe, G. R. (1994) Nucleic Acids Res. 22, 5024-5030], that i s similar to the proline repeat segment of the replication arrest prot ein, Tus, has been determined by H-1 NMR in 50% trifluroethanol. The s tructure is a novel left-handed helix having 5.56 residues per turn an d a regular hydrogen bonding network that is limited to one side of th e helix and contains a channel that runs down the helix axis. The latt er feature gives the structure an overall pipe-like appearance; hence, the structure has been designated a proline pipe helix, The Tus proli ne pipe is also amphiphilic with one side consisting of proline and ot her nonpolar residues while the other side contains mostly basic and o ther polar residues. Tus and several other proteins that contain a sim ilar proline repeat sequence are DNA binding proteins. It is shown her e that the proline pipe helix of TPPI can be accommodated within the m ajor grove of B-form DNA in a manner that positions nearly all of the basic residues near phosphate groups in the DNA backbone, The proline pipe helical motif may be a structural element of many other proteins including integral membrane receptor proteins.