HFIP-induced structures and assemblies of the peptides from the transmembrane domain 4 of membrane protein Nramp1.

Membrane protein Nramp1 (natural resistance-associated macrophage protein 1) is a pH-dependent divalent metal cation transporter that regulates macrophage activation in infectious and autoimmune diseases. A naturally occurring glycine to aspartic acid substitution at position 169 (G169D) within the transmembrane domain 4 (TM4) of Nramp1 makes mice susceptible to Leishmania donovani, Salmonella typhimurium, and Mycobacterium bovis. Here we present a structural and self-assembling study on two synthetic 24-residue peptides, corresponding to TM4 of mouse Nramp1 and its G169D mutant, respectively, in 1,1,1,3,3,3-hexafluoroisopropanol-d(2) (HFIP-d(2)) aqueous solution by nuclear magnetic resonance (NMR) spectroscopy. The results show that amphipathic alpha-helical structures are formed from residue Ile173 to Tyr187 for the wild-type peptide and from Trp168 to Tyr187 for the G169D mutant, respectively. The segment of the N-terminus from Leu167 to Leu172 is poorly structured for the wild-type peptide, whereas it is well defined for the G169D mutant. Both peptides aggregate to form a tetramer and the monomeric peptides in peptide bundles are structurally and orientationally similar. The intermolecular interactions in assemblies could be stronger in the C-terminal regions related to residues Phe180-Leu184 than those in the central helical segments for both peptides. The G169D mutation may change the size of the opening on the termini of assembly. Copyright 2006 Wiley Periodicals, Inc.