Quantum mechanical calculations and experimental measurement of N-terminal charge effects on 1HN and 1HCα chemical shifts in peptides
✍ Scribed by William H. Gmeiner; Julio C. Facelli
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1998
- Tongue
- English
- Weight
- 654 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Niiclmr magnetic resonance .spectro.scopists are increasingl-v utilizing chetnical shlfis to characterize thr secondary strrictiirr of proteins. The present study addresses the effects that the positively chargcd amino group at the N-terminus ?fa peptide hus on ' H N and 'HCa chemical shifis along thci chain. This inf0rmution is necessary for interpreting chemical sh$t data ,/or proteins and/orfi)r peptides that are used as model.r.for protein ~trtictiir~~. The chemical sh& f i l r the 'EI rcsonanccs of:fbiir peptides that difftJr only in the location of their N-terminii are assigned using t~i,o-dirnc.n.cional nmr spectroscopy. The peptides have .sequencc.s dtJrived,from thc /3 srihiinir ofthc glycoprotLYn hormone hiitnun chorionic gonadotropin (hCG-P) . Comparison ofthc 'IIN and the 'HC'cu chctnical shift.s,fi,r r ~s i d u ~s common to all,fi)ur peptide.s rrveals d o ~~& l i / .sh$s, fiJr ' H N and the 'HCa resonances within three residues ?f the N-terminus cotnpured M.it/i chemical sh1fi.s in the interior ofthe peptide. The magnitiidc ofthe downfield shlfi i s largpr,fi,r rcwnances ncurer the N-terminus. Quantum mechanical calciilutions ofthe ' I I N and 'HCa chcmical .shlfifis in peptides constructed with .six alanine units also pwdict a significant trrtniniis crfJi.Lt. Thc calculations agree both qiwlitativrly and quantitatively with the ewpcritnental data. The indiictive nature o f t h e end eflkct is confirmed in the ca1czilation.s by Mulliken population anal-vsis. End eJkcts should be taken into accoiint in determining protrin secondurj< .striict~ires,from circmical shifis. 0 I996 John Wiky & Sons, Inc.