XAO peptide (AcX(2)A(7)O2--NH2; X: diaminobutyric acid side chain, -CH2CH2NH3+; O: ornithine side chain, -CH2CH2CH2NH3+) in aqueous solution shows a predominantly polyproline II (PPII) conformation without any detectable alpha-helix-like conformations. Here we demonstrate by using circular dichroism (CD), ultraviolet resonance Raman (UVRR) and nuclear magnetic resonance (NMR) spectroscopy that sodium dodecyl sulfate (SDS) monomers bind to XAO and induce formation of alpha-helix-like conformations. The stoichiometry and the association constants of SDS and XAO were determined from the XAOSDS diffusion coefficients measured by pulsed field gradient NMR. We developed a model for the formation of XAOSDS aggregate alpha-helix-like conformations. Using UVRR spectroscopy, we calculated the Ramachandran psi angle distributions of aggregated XAO peptides. We resolved alpha-, pi- and 3(10)- helical conformations and a turn conformation. XAO nucleates SDS aggregation at SDS concentrations below the SDS critical micelle concentration. The XAO(4)-SDS16 aggregates have four SDS molecules bound to each XAO to neutralize the four side chain cationic charges. We propose that the SDS alkyl chains partition into a hydrophobic core to minimize the hydrophobic area exposed to water. Neutralization of the flanking XAO charges enables alpha-helix formation. Four XAO-SDS4 aggregates form a complex with an SDS alkyl chain-dominated hydrophobic core and a more hydrophilic shell where one face of the alpha-helix peptide contacts the water environment.