Sequence-specific 1H NMR resonance assignments and secondary structure of human apolipoprotein C-I in the presence of sodium dodecyl sulfate

Apolipoprotein (apo) C-I is a 57-residue exchangeable plasma protein distributed mainly in high and very low density lipoprotein. In this report we present the nuclear magnetic resonance spectra of native apoC-I and synthetic apoC-I, containing selected 15N-labelled amino acids, in the presence of sodium dodecyl sulfate. The proton resonances of apoC-I are assigned and the secondary structure is estimated from the difference of measured alpha-proton chemical shifts to random coil values and the observed NOE interactions. According to these data apoC-I forms two helices, Val-4-Lys-30 and Leu-34-Lys-52, linked by an unstructured region Gln-31-Glu-33. The N-terminal segments of each helix, Val-4-Gly-15 and Leu-34-Met-38, appear to be more flexible than the helical core regions Asn-16-Lys-30 and Arg-39-Lys-52.Key words: 15N-filtered NOESY, chemical shift index, amphipathic helix, lecithin:cholesterol acyltransferase.