Proton Overhauser experiments on kringle 4 from human plasminogen. Implications for the structure of the kringles' hydrophobic core.
1H-NMR Overhauser experiments at 300 and 600 MHz have been implemented on the isolated kringle 4 fragment of human plasminogen. This study shows that Leu46 and Leu77 CH3 delta,delta' groups, as well as two threonine CH3 gamma and a methionine S-CH epsilon (probably Met48) groups, are in efficient dipolar contact with histidine and aromatic side-chains. In particular, the experiments reveal that of the two Leu46 CH3 delta,delta' groups, one is in efficient contact with tryptophan (Trp25 and Trp62) indole rings while the other interacts with a tyrosine (probably Tyr41) phenol. Leu46 appears also to be close to an Ala CH3 beta group. Such a hydrophobic cluster appears to be contiguous to Trp72, hence to Arg71, residues that are through to be part of the lysine-binding site. Acid-base titration experiments show that the buried methionine S-CH3 epsilon group senses a neighboring ionizable group of pK*1 = 3.76, suggesting presence of a carboxyl anionic group (probably an aspartic acid side-chain) in the vicinity of the hydrophobic core. A preliminary model is proposed for the overall folding of the kringle polypeptide chain.
De Marco
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A
Laursen
R A
RA
Llinás
M
M
D000595:Amino Acid Sequence; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D008958:Models, Molecular; D010446:Peptide Fragments / Q000032:analysis*; D010958:Plasminogen / Q000032:analysis*; D011487:Protein Conformation
D010446:Peptide Fragments; D010958:Plasminogen