Folding transitions in calpain activator peptides studied by solution NMR spectroscopy.
Calpastatin, the endogenous inhibitor of calpain, a cysteine protease in eukaryotic cells, is an intrinsically unstructured protein, which upon binding to the enzyme goes through a conformational change. Peptides calpA (SGKSGMDAALDDLIDTLGG) and calpC (SKPIGPDDAIDALSSDFTS), corresponding to the two conserved subdomains of calpastatin, are known to activate calpain and increase the Ca(2+) sensitivity of the enzyme. Using solution NMR spectroscopy, here we show that calpA and calpC are disordered in water but assume an alpha-helical conformation in 50% CD(3)OH. The position and length of the helices are in agreement with those described in the literature for the bound state of the corresponding segments of calpastatin suggesting that the latter might be structurally primed for the interaction with its target. According to our data, the presence of Ca(2+) induces a backbone rearrangement in the peptides, an effect that may contribute to setting the fine conformational balance required for the interaction of the peptides with calpain.
Toke
Orsolya
O
Institute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, 59-67 Pusztaszeri út, Budapest, H-1025 Hungary. toke@chemres.hu
Bánóczi
Zoltán
Z
Tárkányi
Gábor
G
Friedrich
Péter
P
Hudecz
Ferenc
F
D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000737:chemistry; D002154:Calpain / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010455:Peptides / Q000737:chemistry* / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation / Q000187:drug effects; D017510:Protein Folding; D017433:Protein Structure, Secondary
D002135:Calcium-Binding Proteins; D010455:Peptides; C033668:calpastatin; D002154:Calpain; D002118:Calcium