1H-15N Spin–spin couplings in alumichrome

✍ Scribed by Antonio Demarco; Miguell LlináS; Kurt Wuthrich

• Publisher: Wiley (John Wiley & Sons)
• Year: 1978
• Tongue: English
• Weight: 824 KB
• Volume: 17
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1978.360171118

✦ Synopsis

Abstract

We report the determination of two‐ and three‐bond ^1^H‐^15^N spin–spin couplings in the nmr spectra of a polypeptide. The ^1^H‐ and ^15^N‐nmr spectra of 99.2% ^15^N‐enriched alumichrome have been studied at 360 MHz and 10.1 MHz, repectively. While some ^2^J and ^3^J coupling are of the order of 5 Hz, most splitting resulting from the heteronuclear interaction are ≲2 Hz, which introduces strigent requirements of spectral resolution. In the ^1^H spectra these requirements were met by digital deconvolution with a sine bell routine combined with positive exponential filtering. Although the ^15^N spectra clearly exhibit features of fine structure, mainly because of the intrinsic higher nmir sensitivity of protons, observation of ^1^H‐^15^N spin–spin couplings was found to be more practical in the ^1^H than in the ^15^N spectra. We find that the alumichrome data do not satisfy a simple cyclic relationship linking the heteronuclear couplings to the crystallographic ψ dihedral angles. It is suggested that a formal treatment of the ψ‐related interresidue ^1^H‐^15^N coupling might have to take into account a more complex dependence of the intervening ^3^J on the overall local electronic structure, which is dependent on ϕ,ψ, and ω simultaneoulsy. In contrast, our analysis indicates that χ^1^ can be readily determined from the measurement of the corresponding heteronuclear ^3^J coupling in the ^1^H^β^ or in the amide ^15^N resonances. Karplus relationships are proposed that relate this heteronuclear ^3^J to the corresponding dihedral angle θ and which, on average, yield