Solution state structures of human pancreatic amylin and pramlintide.
We have employed pramlintide (prAM) as a surrogate for hAM in CD and NMR studies of the conformational preferences of the N-terminal portion of the structure in media which do not provide long-lived monomeric solutions of hAM due to its rapid conversion to preamyloid beta aggregate states. Direct comparison of hAM and prAM could be made under helix-formation-favoring conditions. On the basis of CD and NMR studies: (i) the Cys(2)-Cys(7) loop conformation has a short-span of helix (Ala(5)-Cys(7)); (ii) the extent to which this helix propagates further into the sequence is medium-dependent; a helix from Ala(5) through Ser(20) (with end fraying from His(18) onward) is observed in aqueous fluoroalcohol media; (iii) in 12+ vol.% HFIP, the amyloidogenic region of hAM forms a second helical domain (Phe(23)-Ser(29)); (iv) the two helical regions of hAM do not have any specific geometric relationship as they are connected by a flexible loop that takes different conformations and (v) although the extreme C-terminus is essential for bioactivity, it is found to be extensively randomized with conformer interconversions occurring at a much faster rate than that is observed in the remainder of the peptide sequence. Two NMR-derived structures of the 1-22 sequence fragment of hAM have been derived. The work also serves to illustrate improved methods for the NMR characterization of helices. A detailed quantitative analysis of the NOE intensities observed in aqueous HFIP revealed alternative conformations in the C-terminal portion of the common amylin helix, a region that is known to be involved in the biorecognition phenomena leading to amyloidogenesis. Even though the SNN sequence appears to be a flexible loop, the chemical shifts (and changes induced upon helix structuring) suggest some interactions between the loop and the amyloidogenic segment of hAM that occur on partial helix formation.
Cort
John R
JR
Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
Liu
Zhihong
Z
Lee
Gregory M
GM
Huggins
K N L
KN
Janes
Susan
S
Prickett
Kathryn
K
Andersen
Niels H
NH
D000595:Amino Acid Sequence; D000682:Amyloid / Q000737:chemistry*; D002021:Buffers; D002942:Circular Dichroism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D058228:Islet Amyloid Polypeptide; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010179:Pancreas / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry*; D017433:Protein Structure, Secondary; D014867:Water / Q000737:chemistry
D000682:Amyloid; D002021:Buffers; D058228:Islet Amyloid Polypeptide; D010446:Peptide Fragments; D014867:Water; C105254:pramlintide