Solution structures of casein peptides: NMR, FTIR, CD, and molecular modeling studies of alphas1-casein, 1-23.
To determine its potential for interacting with other components of the casein micelle, the N-terminal section of bovine alphas1-casein-B, residues 1-23, was investigated with nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopies, and molecular modeling. NMR data were not consistent with conventional alpha-helical or beta-sheet structures, but changes in N-H proton chemical shifts suggested thermostable structures. Both CD and FTIR predicted a range of secondary structures for the peptide (30-40% turns, 25-30% extended) that were highly stable from 5 degrees C to 25 degrees C. Other conformational elements, such as loops and polyproline II helix, were indicated by FTIR only. Molecular dynamics simulation of the peptide predicted 32% turns and 27% extended, in agreement with FTIR and CD predictions and consistent with NMR data. This information is interpreted in accord with recent spectroscopic evidence regarding the nature of unordered conformations, leading to a possible role of alphas1-casein (1-23) in facilitating casein-casein interactions.
Malin
E L
EL
Eastern Regional Research Center, ARS, USDA, Wyndmoor, Pennsylvania 19038, USA. emalin@arserrc.gov
Alaimo
M H
MH
Brown
E M
EM
Aramini
J M
JM
Germann
M W
MW
Farrell
H M
HM
McSweeney
P L
PL
Fox
P F
PF
D002364:Caseins / Q000737:chemistry*; D002942:Circular Dichroism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared
D002364:Caseins; D010446:Peptide Fragments; C098970:isracidin